148 Fun Facts About Sleep

Dolphins sleep with one eye open; what is this slow-wave sleep pattern called?

Unihemispheric slow-wave sleep lets one half of the brain rest while the other stays alert; the eye opposite the sleeping half shuts while the other stays open to keep watch or keep surfacing to breathe.

What is the term for the temporary muscle paralysis that normally occurs during REM sleep?

Atonia is the muscle shutdown of REM sleep, produced by brainstem inhibition of motor neurons; when it fails, sleepers act out their dreams, the hallmark of REM sleep behavior disorder.

Roughly how long did 17-year-old Randy Gardner stay awake for his famous 1964 record?

11 days: Gardner stayed awake about 264 hours ending 8 January 1964, observed by Stanford sleep researcher William Dement, and recovered after a few long sleeps.

Roughly how long does one complete adult sleep cycle, through NREM and REM, last?

90-110 minutes is one pass from light sleep through deep sleep to REM, repeated four to six times a night; REM periods lengthen toward morning, so a short night cuts REM sleep most.

In which country is inemuri, dozing off in meetings, classes or on the train, widely tolerated?

Japan: inemuri joins the words for 'being present' and 'sleep', and a nap in a meeting can be read as proof that someone has worked themselves to exhaustion.

What is the term for the drowsy transitional state while falling asleep, often with vivid imagery?

Hypnagogia is the slide into sleep and hypnopompia its mirror on waking; Salvador Dali and Thomas Edison credited it with ideas, and a 2021 study found a brief dip into it boosted puzzle-solving insight.

Historian Roger Ekirch argued pre-industrial Western Europeans commonly slept in what pattern?

Two segments with a waking gap: a 'first sleep' and 'second sleep' were split by an hour or more around midnight that people used for prayer, chores, sex or conversation.

Which NREM Stage 2 EEG waveform, a sharp negative then slow positive wave, may follow a sudden noise?

K-complexes are large, distinct waveforms primarily seen during NREM Stage 2 sleep, which can occur spontaneously or in response to external stimuli, and are thought to help protect sleep and aid memory.

Which part of the night's sleep is the deepest and most restorative for tissue repair and immunity?

NREM Stage 3, or slow-wave sleep, is when the body repairs tissue and bolsters immunity; it is packed into the first half of the night, so the early hours of sleep do most of the repair work.

Which rare neurological disorder, mostly affecting adolescent males, causes recurring episodes of sleep lasting days or weeks?

Kleine–Levin syndrome can have a teenager sleeping up to 20 hours a day for weeks, yet between episodes they are entirely well, and the attacks usually fade away with age.

Non-24-hour sleep-wake disorder, where the body clock drifts free of the day, is especially common in people with what?

Total blindness leaves no light reaching the retina, so the brain's master clock is never reset to the 24-hour day and the urge to sleep drifts a little later each night.

What term describes a sudden, brief loss of muscle tone triggered by strong emotion, such as laughter?

Cataplexy, a hallmark of type 1 narcolepsy, leaves the person fully conscious during an attack, which can range from a drooping jaw to complete collapse.

Where did body-clock researcher Michel Siffre spend six months of 1972 in isolation?

In a Texas cave: Siffre lived about six months of 1972 in Midnight Cave with no clock or daylight, and his body at times slipped onto a 48-hour day that he could not tell from a normal one.

REM sleep behavior disorder, acting out dreams, is a strong early predictor of which condition?

Parkinson's disease: RBD can begin years or decades before tremor and stiffness, and a majority of people with RBD go on to develop Parkinson's or a related synucleinopathy.

In classical myth, which underworld river flows through the cave of the god of sleep?

Lethe: Ovid has its waters trickle over pebbles at the foot of Sleep's cave, their murmur inviting slumber; in myth, anyone who drank from the river forgot everything.

Fatal familial insomnia, an inherited disease that destroys the ability to sleep, belongs to which class of disorders?

Prion diseases: in FFI a misfolded protein, from the same gene behind inherited Creutzfeldt-Jakob disease, destroys the thalamus, so sleep fails entirely and death follows within months to a few years.

What disorder involves recurrent upper airway obstruction while a person is asleep?

Sleep apnea can stop a sleeper's breathing more than 30 times an hour in severe cases; each pause ends in a brief arousal they rarely remember, so a bed partner often notices first.

Which chronic neurological condition causes overwhelming daytime sleepiness and sleep attacks?

Narcolepsy: type 1 involves the loss of roughly 70,000 orexin (hypocretin) neurons in the hypothalamus, which is why low orexin in spinal fluid confirms the diagnosis.

Which is the most common sleep disorder among adults?

Insomnia is the most common sleep complaint, and the first-line treatment is not a pill but CBT-I, a short course of therapy that retrains habits and beliefs about sleep.

Which chronic neurological disorder is also known as Willis–Ekbom disease?

Restless Legs Syndrome, or Willis–Ekbom disease, brings an urge to move the legs that builds at rest in the evening and eases with walking; low iron in the brain is one known driver.

What is the medical term for sleepwalking?

Somnambulism arises from deep sleep early in the night, not from dreams; despite the eyes-closed, arms-out cliche, a sleepwalker's eyes are open, and they rarely recall the episode.

Which theory says dreams are the brain making sense of random brainstem signals in REM sleep?

Activation-synthesis theory, from Harvard psychiatrists Allan Hobson and Robert McCarley in 1977, holds that the forebrain builds each dream by matching random brainstem signals against stored memories.

Which sleep disorder, often with a felt presence or chest pressure, strikes while falling asleep or waking?

Sleep paralysis happens when the muscle shutdown of REM sleep lingers into waking, so the mind is alert while the body cannot move; episodes pass within a few minutes.

Chronic sleep deprivation significantly increases the risk of which of the following health conditions?

Type 2 diabetes: people on restricted sleep clear glucose more slowly and show reduced insulin sensitivity, and habitual short sleep is also tied to weight gain and heart disease.

In 1953, graduate student Eugene Aserinsky discovered REM sleep while working at which institution?

University of Chicago: Aserinsky, working under Nathaniel Kleitman, spotted the rapid eye movements of sleeping subjects there; their 1953 Science paper founded modern sleep research.

What is the recommended sleep duration for adults aged 18 to 64 per night?

7-9 hours is the National Sleep Foundation's 2015 recommendation for adults 18-64; newborns need 14-17 hours, and habitual sleep under seven hours is linked to coronary heart disease.

Which brain structure is the master pacemaker of the mammalian circadian clock?

The suprachiasmatic nucleus (SCN) sits just above the crossing of the optic nerves, so it gets light signals straight from the eyes; people with damage to it sleep erratically across the day.

What other name for REM sleep did French researcher Michel Jouvet coin in 1959?

Paradoxical sleep: the EEG looks almost like waking, rapid and low-voltage, while the voluntary muscles are switched off; Michel Jouvet coined the term in 1959.

What is the sudden, involuntary muscle twitch that can occur just as a person is falling asleep?

A hypnic jerk, or sleep start, often comes with a sensation of falling; most people get them now and then, and caffeine, stress or fatigue make them more frequent.

Which of these habits do sleep-hygiene guidelines recommend?

A consistent bedtime and wake-up time, weekends included, steadies the body clock; a nightcap fragments the second half of the night, and after 20 minutes awake the advice is to get out of bed.

What sleep study records brain waves, eye movements, muscle activity and breathing overnight?

Polysomnography (PSG) wires a sleeper with sensors on the scalp, eyelids, chin and chest for a full night; a scorer then reads the recording in 30-second slices to map every sleep stage.

Which wake-promoting brain chemical do older, drowsy-making allergy pills block?

Histamine neurons in the hypothalamus fire fastest during waking and fall silent in sleep; older antihistamines cross into the brain and block their signal, which is why they cause drowsiness.

Which colour of evening screen glow does most to suppress melatonin?

Blue light: wavelengths around 460-480 nm, sensed by melanopsin cells in the retina, suppress melatonin most, and the effect grows with brightness and duration of exposure.

Which hormone's biggest daily surge comes with the first bout of deep sleep?

Growth hormone surges with the first plunge into deep sleep, one reason chronic short sleep is thought to hamper tissue repair in adults and growth in children.

What is the term for a dream in which the dreamer knows they are dreaming and may steer it?

Lucid dreaming was confirmed in the lab in 1975, when a sleeper signalled to researchers from inside a dream using eye movements agreed in advance.

What are brief, unintended episodes of sleep that occur during a person's waking hours?

Microsleep lapses last only seconds, sometimes with the eyes still open, and people often don't realise one has happened, which is what makes them so dangerous behind the wheel.

What is the name of the graph produced during a sleep study that plots the stages of sleep against time?

A hypnogram plots sleep stages against time; a typical night shows four to six cycles, with deep sleep concentrated early and REM periods lengthening toward morning.

What are the brief high-frequency brain-wave bursts of NREM Stage 2 called?

Sleep spindles fire at about 12 to 14 Hz for half a second or more, generated by the thalamus, and are linked to memory consolidation and to screening out noise during sleep.

What is the cumulative effect of repeatedly getting too little rest over an extended period?

Sleep debt builds night by night and is not wiped out by one lie-in: recovery can take several days, and a 2019 study found weekend catch-up sleep failed to undo the metabolic harm.

Which small brain gland is nicknamed the 'third eye'?

The pineal gland sits deep in the centre of the brain, yet it tracks daylight: fed day-and-night cues from the eyes, it releases melatonin once darkness falls, one reason given for the nickname.

What system, active during sleep, is responsible for clearing metabolic waste products from the brain?

The glymphatic system pumps fluid through brain tissue to carry off waste; a 2013 mouse study found the gaps between brain cells widen by about 60% in sleep, speeding the removal of beta-amyloid.

Which parasomnia makes a person hear an imagined gunshot or cymbal crash while drifting off?

Exploding head syndrome sounds alarming but involves no pain and is considered harmless; some people also see a flash of light with the imagined bang.

What is the term for being a 'lark' or an 'owl', your natural timing for sleep?

Chronotype is your built-in propensity to sleep at a particular point in the day; 'larks' and 'owls' mark its extremes, and it tends to shift later in adolescence.

What is the physiological term for the amount of time it takes to fall asleep once in bed?

Sleep latency in a well-rested adult runs about 10 to 20 minutes; dropping off within five is no gift but a sign of severe sleep deprivation.

What term describes external cues like daylight that reset the body clock?

Zeitgebers, German for 'time-givers', include meal times, exercise and social contact as well as daylight; cut off from all of them, the body clock runs free and drifts off the 24-hour day.

What is the grogginess and disorientation felt immediately after waking up called?

Sleep inertia is worst when the alarm cuts into deep sleep and usually fades within half an hour, which is why naps are best kept under 30 minutes.

What is the increase in dreaming sleep on recovery nights after being deprived of it called?

REM rebound: after nights of lost REM, people reach it sooner and spend more of the night in it, evidence that the brain keeps a tally of the stage; stress can set it off too.

Which bedside device is the first-line treatment for breathing that keeps stopping in sleep?

A CPAP machine holds the airway open with mild continuous positive airway pressure, and it only keeps working if used for every sleep, naps included.

Which rare disorder brings heavy drowsiness by day and long, unrefreshing naps despite adequate night-time sleep?

Idiopathic hypersomnia makes waking the hard part: even after a long night, many sufferers fall straight back asleep or surface confused and irritable.

Brain recordings in 2016 proved which seabirds sleep on the wing during ocean flights lasting up to 10 days?

Frigatebirds do sleep in flight, sometimes with the whole brain at once, but for well under an hour a day, a small fraction of the sleep they take on land.

Which slow EEG waves, below 4 Hz, define stage N3 sleep?

Delta waves dwindle with age, so older people spend less time in stage N3, one reason they wake several times a night.

Which EEG rhythm, at 8 to 12 Hz, dominates in relaxed wakefulness with the eyes closed?

Alpha waves at 8 to 12 Hz appear over the occipital cortex in relaxed wakefulness with eyes closed; their breakup into slower theta activity marks the onset of stage N1 sleep.

What does the Epworth scale, scored from 0 to 24, measure?

Daytime sleepiness: the Epworth Sleepiness Scale, devised by Melbourne doctor Murray Johns, asks how likely you are to doze off in eight everyday situations, each scored 0 to 3.

Which age group spends by far the largest share of its sleep in REM?

Newborns spend at least half their sleep in REM, against an adult's 20–25%; researchers think the stage supplies the stimulation a developing brain needs to wire itself.

In which Shakespeare play does the title character hear a voice cry 'Sleep no more!' after murdering a king?

Macbeth has just stabbed the sleeping King Duncan when he hears it; the same speech calls sleep the balm of hurt minds, and his wife later walks the castle in her sleep.

Which brain region largely switches off during REM sleep, one reason dreams go unquestioned?

The dorsolateral prefrontal cortex, seat of working memory and self-monitoring, shows markedly reduced blood flow in PET scans during REM sleep, while the amygdala and visual areas light up.

Which of these mammals sleeps the least, under five hours a day?

Giraffes sleep only about 4.6 hours a day in zoo studies, mostly in short bouts; for brief spells thought to be REM sleep they lie down and bend the neck back to rest the head on the hindquarters.

Brain recordings of which wild animal in 2008 showed it sleeps under 10 hours a day, far less than in zoos?

The sloth, recorded wild in a rainforest canopy with miniature brain-wave loggers, slept only about 9.6 hours a day, over six hours less than captive sloths, so its lazy reputation owes much to the zoo.

Which insects have been shown to use sleep to store long-term memories?

Honeybees: a 2012 Berlin study found bees deprived of sleep after learning a new route failed to retain it, evidence that sleep consolidates their navigation memory.

A 2017 study found which mammal sleeps only about two hours a day in the wild?

African elephant: two wild matriarchs in Botswana tracked with trunk-mounted activity meters in a 2017 study averaged about two hours of sleep a day and once went 46 hours without any.

Which mammal shows the largest amount of REM sleep known in any animal?

REM activity in the platypus never reaches the forebrain, so the egg-laying mammal probably does not dream.

Killer whales and bottlenose dolphins barely sleep, a 2005 study found, during which period?

Their first month of life: a 2005 Nature study found the calves and their mothers alike kept swimming 24 hours a day, then took several months to build up to normal adult rest.

Which ducks in a sleeping row most often keep one eye open?

The ones on the outer edge: in a 1999 Nature study, mallards at the ends of a row slept with one eye open far more often, the open eye facing outward to watch for threats.

An octopus's 'active sleep' stage, full of eye and body movement, lasts roughly how long?

About 1 minute: in a 2023 Nature study, Octopus laqueus cycled roughly every hour from pale-skinned 'quiet sleep' into a minute-long burst of colour-flashing, eye-moving 'active sleep'.

In 2016, REM- and NREM-like sleep stages were reported in which reptile?

Bearded dragon: Gilles Laurent's Frankfurt lab reported in Science that Pogona vitticeps cycles between slow-wave and REM-like states about every 80 seconds; two-stage sleep had been thought unique to birds and mammals.

The word 'siesta' comes from a Latin phrase naming which hour, counted from dawn?

Sixth: siesta comes from Latin hora sexta, the sixth hour after dawn, about noon, when Romans paused for the heat of the day.

Which organisation's study of long-haul pilots found a cockpit nap of about 26 minutes sharpened alertness?

NASA gave long-haul crews a planned 40-minute rest in the cockpit seat; pilots slept about 26 minutes on average and stayed more alert than crews without one, so a short doze is still called a NASA nap.

In Greek myth, Hypnos, the personification of sleep, is the twin of which figure?

Thanatos, the personification of death, is Hypnos's twin; in the Iliad the pair carry Zeus's fallen son Sarpedon from the battlefield at Troy home to Lycia for burial.

In Ovid, which son of Sleep specialised in appearing in dreams in human form?

Morpheus: in Ovid's Metamorphoses he is the son of Sleep who takes human form in dreams, while Phobetor becomes beasts and Phantasos inanimate things; morphine is named after him.

In the Iliad, which goddess bribes Hypnos with a bride to lull Zeus to sleep?

Hera swears by the river Styx to give Hypnos the Grace Pasithea as his wife; he took persuading, having once fled to his mother Night after an earlier trick on Zeus.

In Andersen's 1841 tale, the Sandman is called Ole Lukøje, a surname meaning what?

Shut-eye: Lukøje is Danish for 'close-eye', so Andersen's Sandman is Ole Shut-Eye; he carries two umbrellas, a painted one for good children and a blank one for the naughty.

The phrase 'jet lag' first appeared in print in 1966 in which newspaper?

Writer Horace Sutton called it 'a debility not unakin to a hangover' that comes from jets leaving your rhythms behind.

On average, how long does the body need to reset for each hour of time-zone change?

One day: the rule of thumb is about a day of adjustment per time zone crossed; morning light advances the clock for eastward trips, evening light delays it for westward ones.

Most travellers find jet lag harder to shake after flying in which direction?

East: flying east forces a phase advance, and the body clock, which naturally runs slightly longer than 24 hours, adjusts more easily to delays than to advances.

Which drink's maker sponsored Nathaniel Kleitman's early sleep research?

Ovaltine: the Wander Company, maker of the malted bedtime drink, funded Kleitman's Chicago work in the 1930s, hoping it could be sold as a remedy for sleeplessness.

At which Kentucky landmark did Kleitman run a 32-day sleep experiment in 1938?

Mammoth Cave: in 1938 Kleitman and student Bruce Richardson lived 32 days underground there trying to adopt a 28-hour day; he later studied sleepers in submarines and above the Arctic Circle.

The wake-promoting neuropeptide orexin takes its name from the Greek for what?

Appetite: Sakurai's team coined orexin from Greek orexis in 1998 because it stimulated feeding in rats; a rival team found the same molecule and called it hypocretin.

An orexin receptor mutation causes an inherited sleep-attack disorder in which dog breed?

Doberman Pinscher: Emmanuel Mignot's Stanford colony of narcoleptic Dobermans led to the 1999 discovery of a hypocretin (orexin) receptor-2 mutation, showing how central orexin is to staying awake.

The 2017 Nobel Prize for circadian-clock mechanisms honoured work on which organism?

Fruit fly: Jeffrey Hall, Michael Rosbash and Michael Young traced the daily rise and fall of the period gene's protein in Drosophila, the fruit fly, sharing the 2017 Nobel Prize in Physiology or Medicine.

Caffeine keeps you awake by blocking the receptors of which drowsiness-building molecule?

Adenosine builds up during waking hours and promotes drowsiness; caffeine is shaped alike enough to sit in adenosine receptors without switching them on.

The Z-drug zolpidem, approved in the US in 1992, is sold under which brand name?

Ambien: zolpidem shortens the time to fall asleep only modestly, and guidelines put behavioural therapy first; some users have got out of bed and driven, cooked or made phone calls with no memory of it.

Which country, with Austria-Hungary, first adopted nationwide daylight saving in 1916?

Germany: on 30 April 1916 Germany and Austria-Hungary became the first nations to adopt daylight saving, to save wartime coal; Britain followed three weeks later and the United States in 1918.

In orbit, what do International Space Station astronauts sleep in?

Tethered sleeping bags: each astronaut hooks a bag to the wall of a small cabin so they don't drift off; even so, a 2014 study found station crews average only about six hours' sleep a night.

In 1992, which country's top court upheld sleepwalker Kenneth Parks's acquittal for killing his mother-in-law?

Canada: the Supreme Court upheld Kenneth Parks's acquittal, accepting that he had driven to his in-laws' home and attacked them while sleepwalking, a state the law calls non-insane automatism.

The 'mare' in nightmare is no horse: in old European folklore, it named what creature?

A chest-sitting demon: the mare of Germanic folklore was a spirit that sat on sleepers and gave them bad dreams, so 'nightmare' first named the creature and only later the dream itself.

Aaron Lerner isolated the night hormone in 1958 after cow-gland extract did what to frogs?

Lightened their skin: dermatologist Aaron Lerner, hunting a treatment for skin disease, found that cow pineal extract blanched frog skin, and built the name melatonin on the Greek melas, 'dark'.

A 2000 study likened 17–19 hours awake to a moderate dose of what?

Alcohol: Williamson and Feyer found 17 to 19 hours awake slowed people as much as a 0.05% blood-alcohol level, the legal driving limit in many countries, and longer spells matched 0.1%.

Maureen Weston's 1977 record of 449 hours awake was set in what kind of marathon?

Rocking-chair: Maureen Weston of Peterborough, England, stayed awake 449 hours, 18 days and 17 hours, in a 1977 rocking-chair marathon; Guinness later stopped certifying such attempts as too dangerous.

Which migrating bird's knack for going weeks on little sleep was studied with US Department of Defense funding?

White-crowned sparrow: Niels Rattenborg's team found captive sparrows in migratory restlessness slept about two-thirds less for weeks yet kept their accuracy on learning tasks, a feat since studied for human alertness.

In Greek legend, which Cretan seer dozed off in a cave while hunting a stray sheep and woke decades later?

Epimenides, in Diogenes Laertius's telling, slept 57 years and woke to find the farm in a stranger's hands and his younger brother an old man.

A 77,000-year-old bed of sedges and insect-repellent leaves was found at Sibudu Cave in which country?

South Africa: the bedding at Sibudu Cave in KwaZulu-Natal, reported in Science in 2011, layered sedges with Cryptocarya woodii leaves, a natural insecticide that probably kept mosquitoes off the sleepers.

The best-known classical lullaby, 'Wiegenlied' of 1868, is by which composer?

Brahms wrote his Wiegenlied, Op. 49 No. 4, in 1868 for his friend Bertha Faber's second son; in 2000 a chest physician asked in a medical journal whether the composer himself had a sleep-breathing disorder.

Which scholar wrote in 1508 that one man's yawning makes another yawn?

Erasmus: the 1508 Venice edition of his Adagia records that one man's yawning makes another yawn; a later French proverb claimed one good gaper makes seven others gape.

Mask-pressure therapy for obstructed breathing in sleep was first described in which city?

Sydney: Colin Sullivan of Royal Prince Alfred Hospital reported in The Lancet in 1981 that air blown gently through a nose mask kept five patients' airways open all night; until then the drastic remedy was a tracheotomy.

Excessive teeth grinding or jaw clenching, often during sleep, is known medically as what?

Bruxism, from Greek brychein 'to gnash', affects many sleepers who have no idea they do it; the first clue is often a partner's complaint or a dentist spotting worn enamel.

Which small primate was shown in 2004 to hibernate in tropical tree holes for seven months a year?

Lemur: Madagascar's fat-tailed dwarf lemur lies torpid in tree holes through the dry season, living off fat stored in its tail, even though temperatures there climb above 30 °C.

In captivity, which of these mammals sleeps least, under three hours a day?

Horse: horses doze standing, thanks to a locking 'stay apparatus' in their legs, and total under three hours' sleep a day, but they must lie down to reach REM sleep.

Which hormone typically rises through the night to peak around waking time, then falls during the day?

Cortisol climbs through the second half of the night and peaks within an hour of waking, then falls through the day; melatonin runs the opposite course, rising after dark.

Which Australian marsupial sleeps twenty hours a day because its leafy diet gives so little energy?

The koala dozes so long because eucalyptus leaves are low in energy and slow to digest. A single meal can stay in its gut for 100 hours or more.

Sea otters often wrap themselves in what while resting, so they do not drift out to sea?

Kelp works as an anchor line: an otter rolls itself in the fronds and floats on its back without being carried off. Mothers wrap their pups in it too while they dive for food.

Which Beatles song, first titled 'Scrambled Eggs', came to Paul McCartney as a melody in a dream?

Yesterday arrived so complete that McCartney spent about a month asking people in the music business whether they had heard it before. He feared he had copied it without knowing.

Which novel grew from a 'waking dream' its teenage author had beside Lake Geneva in 1816?

Frankenstein began when Lord Byron suggested that his guests each write a ghost story. Mary Shelley, unable to sleep after midnight, saw the tale's 'grim terrors' in her imagination.

Which amino acid in turkey is wrongly blamed for drowsiness after Thanksgiving dinner?

Tryptophan gets the blame, yet turkey holds about as much of it as other meats. The sleepy feeling owes more to everything else on the plate, above all the carbohydrates.

Which mattress material was developed in 1966 for NASA to make aircraft cushions safer?

Memory foam came out of NASA's Ames Research Center, not a bedding firm. The agency released it to the public domain in the early 1980s, and mattress makers took it from there.

Which African insect spreads the parasite that causes the deadly disease known as sleeping sickness?

The tsetse fly passes on the parasite Trypanosoma brucei when it bites. Once the infection reaches the brain it turns the body's timetable upside down: drowsy days, wakeful nights.

In 'The Wizard of Oz', the Wicked Witch casts a sleeping spell over a field of which flowers?

Poppies send Dorothy to sleep just before she and her friends reach the Emerald City. The fake snow that covers her in the 1939 film was made of white gypsum.

In industrial Britain, a 'knocker-up' walked the streets with a long bamboo stick to do what?

The job was to wake sleeping workers by tapping on bedroom windows, in an age when alarm clocks were neither cheap nor reliable. Mary Smith of London fired dried peas at the glass instead.

Which inventor boasted of sleeping four hours a night yet reputedly napped with a ball in each hand?

Thomas Edison is said to have held the balls so that they would drop and wake him as he nodded off. A 2021 study found that this twilight state just before sleep can help solve a hard problem.

The US National Sleep Foundation recommends 8 to 10 hours of sleep a night for which age group?

Teenagers sit in the middle of the foundation's table, which starts at 14 to 17 hours for newborns and shrinks with each age band. The figures followed a two-year review of the evidence.

The American Academy of Pediatrics wants middle and high schools to start no earlier than what time?

8:30 a.m. was the academy's floor because puberty pushes the sleep of adolescents later, so an early bell cuts the night short. Schools that made the switch saw attendance and test scores rise.

Which seahorse-shaped brain structure replays the day's events during deep sleep to store them as memories?

The hippocampus re-runs the day at speed while the body lies still. In a rat that has explored a maze, the same place cells fire again in sequence, forwards or in reverse, compressed several-fold in time.

Which peanut-sized structure deep in the brain holds the nerve cells that control sleep and waking?

The hypothalamus is tiny but busy: it also governs body temperature, hunger and thirst. Some of its cells promote sleep by releasing GABA, a chemical that quietens the brain's arousal centres.

Which ocean giant has been seen sleeping in pods that hang vertically, heads just below the surface?

The sperm whale sleeps upright in short bouts, and a 2008 study suggested it may rest both sides of the brain at once. Deep sleep seems to fill only about 7 percent of its time.

Scientists who fitted brain-wave recorders to which soaring seabird found that it sleeps in mid-air?

The frigatebird naps while climbing on rising air, usually with one half of its brain at a time. Its mid-air sleep came to about 40 minutes a day, almost all of it at night.

Which colourful reef fish blows a cocoon of mucus around itself at night before settling to rest?

The parrotfish pushes the mucus out of its mouth until the cocoon envelops it. The wrapping is thought to hide its scent, and to warn it when a moray eel disturbs the membrane.

Which brainless sea animal was the first creature without a central nervous system observed sleeping?

The jellyfish that did it is Cassiopea, the upside-down jelly. Its dozing is evidence that sleep does not require a brain at all.

Which drug, first sold in 1957 for anxiety and trouble sleeping, caused thousands of birth defects?

Thalidomide was sold over the counter and was also promoted for morning sickness, which put it in the hands of pregnant women. The disaster led many countries to tighten their drug regulation.

What is the medical name for the crusty 'sleep' that gathers in the corners of the eyes overnight?

Rheum is a thin mucus that the eyes shed all day long. While a person is awake, blinking washes it away with tears; overnight nothing clears it, so it dries into a crust.

In Washington Irving's tale, Rip Van Winkle dozes off for twenty years and sleeps through which war?

The American Revolution passes him by completely. Back in his village he declares himself a loyal subject of George III, unaware that the king no longer rules there.

Which Shakespeare character muses 'To sleep, perchance to dream' while weighing whether to go on living?

Hamlet speaks the line in his 'To be, or not to be' monologue. Death tempts him as a kind of sleep, but the dreams it might bring are 'the rub' that makes him hesitate.

Which princess in Tchaikovsky's 'The Sleeping Beauty' pricks her finger and sleeps for 100 years?

Aurora was cursed to die on her sixteenth birthday; the Lilac Fairy cannot undo the spell of the wicked Carabosse, only soften it into a century of sleep. Disney kept the name for its 1959 princess.

In Genesis, whose dream of seven fat cows eaten by seven lean cows does Joseph interpret?

Pharaoh learned that the cows stood for seven years of abundance followed by seven of famine. Joseph's advice to store the surplus grain raised him to second-in-command of Egypt.

Which dystopian novel has children conditioned by 'hypnopaedia', slogans played to them as they sleep?

Brave New World uses sleep-teaching to make every caste content with its place. In the story it failed at teaching facts, then proved ideal for planting moral attitudes.

Which Coleridge poem was, by his account, composed in an opium dream and cut short by a caller from Porlock?

Kubla Khan was meant to run to 200 or 300 lines, Coleridge said, but the interruption made him forget the rest. His manuscript note admits to two grains of opium.

Which picture book by Margaret Wise Brown follows a rabbit's bedtime ritual in a 'great green room'?

Goodnight Moon stars rabbits only because illustrator Clement Hurd drew them better than people. The author took the idea from bidding her own nursery toys goodnight as a child.

Which guest at the Mad Hatter's tea party in 'Alice's Adventures in Wonderland' keeps falling asleep?

The Dormouse is being used as a cushion by the other two when Alice arrives. It wakes just long enough to tell a tale of three sisters who live in a treacle well.

In the poem 'A Visit from St. Nicholas', visions of what dance in the heads of the sleeping children?

Sugar plums often held no fruit at all: they were small hard sweets, built up around a seed, nut or spice. The children dreaming of them are 'nestled all snug in their beds'.

Which fictional detective makes his first appearance in Raymond Chandler's novel 'The Big Sleep'?

Philip Marlowe's debut takes its title from a euphemism for death: the last pages speak of 'sleeping the big sleep'. Humphrey Bogart played him in the 1946 film.

Which horror villain murders people through their dreams in the film 'A Nightmare on Elm Street'?

Freddy Krueger is the spirit of a child killer burned to death by his victims' parents. Anyone he catches asleep dies for real, so staying awake is the only defence.

In Christopher Nolan's film 'Inception', which object does Cobb use to check that he is no longer dreaming?

A spinning top that never falls would mean Cobb is still inside a dream. He walks away before he can see the result, and the script ends with the top 'STILL SPINNING'.

Which sci-fi film grew from a fever dream in Rome of a metallic torso dragging itself from an explosion?

The Terminator came to James Cameron while he lay ill during the release of his first film, 'Piranha II'. He used the nightmare image as a 'launching pad' for a slasher-style script.

Which heavy metal band opened its 1991 album with 'Enter Sandman', a song about a child's nightmares?

Metallica also released the song as the album's lead single. The lyrics about a child's bad dreams were written by vocalist and guitarist James Hetfield.

Which pop artist's silent film 'Sleep' shows John Giorno sleeping for more than five hours?

Andy Warhol reached five hours and 21 minutes by looping his footage: in the third reel a single shot of four and a half minutes repeats for an hour and a half.

Which British artist's own unmade bed, shown at the Tate in 1999, was shortlisted for the Turner Prize?

Tracey Emin drew 'My Bed' from a low spell in which she stayed in bed for four days, drinking and not eating. The installation sold at auction in 2014 for more than £2.5 million.

In which city did newlyweds John Lennon and Yoko Ono stage their first 'Bed-In for Peace' in 1969?

Amsterdam's Hilton hosted the honeymoon protest: for a week the couple invited the world's press into their room from 9 a.m. to 9 p.m. A second bed-in in Montreal produced 'Give Peace a Chance'.

Which French painter's 'The Sleeping Gypsy' shows a lion musing over a woman asleep on a moonlit night?

Henri Rousseau described her as a wandering mandolin player 'overcome by fatigue in a deep sleep'. The 1897 canvas now hangs in the Museum of Modern Art in New York.

Which doctor called the interpretation of dreams 'the royal road' to knowledge of the unconscious mind?

Sigmund Freud argued that a dream expresses an unconscious wish in disguise. His book on the subject was first printed in an edition of 600 copies, which took eight years to sell out.

Which type of bed did design student Charles Hall create in 1968 at San Francisco State University?

The waterbed began as Hall's attempt at an innovative chair: his first prototype was a vinyl bag filled with 300 pounds of cornstarch. He patented the bed in 1971 as a 'liquid support for human bodies'.

August Kekulé said a daydream of a snake seizing its own tail showed him the ring shape of which molecule?

Benzene has six carbon atoms, and Kekulé proposed in 1865 that they join in a closed ring. The tail-biting snake of his reverie is an ancient symbol, the ouroboros.

The word 'mattress' comes from a word meaning 'the thing thrown down' in which language?

Arabic 'al-matrah' named the large cushion or rug thrown down to lie on. The word was borrowed in medieval Sicily and reached English by way of Italian and Old French.

The world's first capsule hotel, with sleeping pods instead of rooms, opened in 1979 in which Japanese city?

Osaka got the first one because a local sauna operator wanted somewhere proper for customers who had missed the last train. He hired architect Kisho Kurokawa to design it.

Which neurologist's book 'Awakenings' told the life stories of survivors of the 'sleepy sickness' epidemic?

Oliver Sacks wrote up the case histories of patients struck by encephalitis lethargica. In the 1990 film of the book, Robin Williams plays a doctor based on him opposite Robert De Niro.

Which mill owner of New Lanark coined the slogan 'Eight hours' labour, eight hours' recreation, eight hours' rest'?

Robert Owen had the slogan by 1817, years after he first demanded a ten-hour day and brought it in at his own mills. The Welsh textile manufacturer was also a founder of the co-operative movement.

What is the Japanese word for napping in public or at work, often read as a sign of dedication?

Inemuri can be excused even at a desk, writes scholar Brigitte Steger, because it suggests the napper stayed up late working or has worked to the point of complete exhaustion.

Which composer's 2015 album 'Sleep' is an eight-and-a-half-hour lullaby meant to be heard overnight?

Max Richter consulted neuroscientist David Eagleman about how the brain works at night while he wrote it. A one-hour version, 'From Sleep', was released alongside it.

The dreamcatcher, first made as a protective charm for infants, is a hoop woven to replicate what?

A spider web was the model because, in an Ojibwe legend recorded in 1929, the charms began with Spider Woman, who takes care of the children. The idea spread widely in the 1960s and 1970s.

Cornell psychologist James Maas coined which two-word term for a short daytime sleep meant to restore alertness?

Power nap is the name Maas gave to a brief doze that is timed to end before deep slow-wave sleep begins, so the napper wakes quickly revitalised.

Which bed, hinged to store upright against a wall, did a San Francisco inventor file patents for around 1900?

The Murphy bed, legend has it, let William Murphy court an opera singer in his one-room apartment: with the bed folded away, his bedroom became a respectable parlour.