How long can you go without sleep? And can anyone live on 2 hours a night?
The documented record is 11 days awake. Rats die within weeks, and no one has been shown to thrive on 2 hours a night. What research knows about the limits of sleep.
How long can a human go without sleep?
The number most often quoted is 11 days. In the famous case of Randy Gardner, one person stayed awake for 264 hours.[1] A systematic review of sleep deprivation studies lists it as the longest one, with a single participant.[2] Motivated volunteers can be kept awake for days if they stay busy with things they enjoy.[1]
That figure is a record, not a limit. It comes from an era when such experiments were still done. Today, keeping people awake for more than 48 hours is considered unethical, and in most countries it is prohibited by law, so the review had to rely on historical studies.[2] The most common length in those studies was three to four nights.[2]
Staying awake also isn’t quite what it sounds like. People who have gone without sleep for a long time can look awake, moving around with their eyes open, while their brain waves slow down or slip into brief microsleeps. Seriously sleep-deprived people have been reported to fall asleep even in dangerous situations.[1]
What happens to your body, hour by hour
The damage doesn’t start on day three. It starts on an ordinary long day.
Hours awake
- Hours 0–16 An ordinary waking day
- Hours 16–24 Attention lapses add up; at 17 to 19 hours, some tests as bad as with 0.05% blood alcohol
- Hours 24–48 Perception slips: distorted vision, anxiety, losing track of time
- From hour 48 Hallucinations from 48 hours, delusions from 72
When symptoms began in the studies; people differ, and the stages overlap. Complex hallucinations were reported from 48 to 90 hours. Source: [3, 4, 2]
Show the numbers
| An ordinary waking day | Hours 0–16 |
|---|---|
| Attention lapses add up; at 17 to 19 hours, some tests as bad as with 0.05% blood alcohol | Hours 16–24 |
| Perception slips: distorted vision, anxiety, losing track of time | Hours 24–48 |
| Hallucinations from 48 hours, delusions from 72 | From hour 48 |
After about 16 hours. In a lab study with 48 healthy adults, lapses of attention rose almost in a straight line with every hour spent awake beyond about 15.8 hours, no matter whether the hours came from one sleepless night or from many short ones.[3]
After 17 to 19 hours. In one study, 39 transport workers and soldiers were tested over 28 hours without sleep, and also after measured amounts of alcohol. After 17 to 19 hours awake, around 10:30 pm to 1 am, their performance on some tests was as bad as at a blood alcohol level of 0.05%, or worse. On some tests, responses were up to 50% slower. Kept awake longer, they reached the level of the highest dose they were given, 0.1%.[4]
From the first night. A review of 21 sleep deprivation studies found that perception starts to slip quickly: distorted vision, anxiety, irritability, feeling detached from yourself, losing track of time, all within 24 to 48 hours. Complex hallucinations and disordered thinking followed after 48 to 90 hours, delusions after 72. By then the picture resembled acute psychosis. A period of normal sleep made these symptoms go away in many cases, though not in all.[2]
Can you die from lack of sleep?
In animals, yes. In a classic experiment, rats were kept awake with mild physical stimuli. Control rats received the same stimuli, timed so that they could still sleep. The sleep-deprived rats developed severe illness and died. The control rats did not.[5] Rats kept awake this way, on a disk over water, die after 2 to 4 weeks, and prolonged sleep deprivation is also fatal in flies and cockroaches.[1]
What exactly kills them is still unclear. Death might come from the lost sleep itself or from the stress of being woken over and over.[1] A 2020 study in flies offered one answer: without sleep, reactive oxygen species built up in the gut, and when the researchers neutralised them, flies lived a normal lifespan with little to no sleep. In mice, the same build-up appeared in the gut.[9]
In humans, no such experiment can be done. The closest case is fatal familial insomnia, an inherited disease: patients die after developing a syndrome not unlike that of the sleep-deprived rats.[1] Because it is a disease, it can’t tell us how long a healthy person would last. The honest answer is that nobody knows.
Can you live on 2 hours of sleep a day?
There is no evidence that anyone can. Advocates of polyphasic sleep, which splits sleep into several short episodes across the day, claim to thrive on as little as 2 hours in total. A panel of the US National Sleep Foundation went through 40,672 publications to check. Only 22 were relevant, and they found no evidence of a benefit. The panel concluded that these schedules, and the sleep loss built into them, are linked to worse physical health, mental health and performance.[6]
Short sleepers do exist, but they are rare and they don’t sleep 2 hours. Geneticists call them natural short sleepers: people who all their lives sleep 4 to 6 hours a night and feel rested.[7]
| Sleep per 24 hours | Who | What is documented |
|---|---|---|
| About 2 hours | Polyphasic sleep advocates | A claim. No study found a benefit.[6] |
| 4 to 6 hours | Natural short sleepers | Lifelong, and they feel rested. One lab had found more than 50 such families by 2019.[7] |
| 6.25 hours on average | Two carriers of a DEC2 gene variant | Their relatives without it: 8.06 hours.[10] |
| 7 hours or more | Recommendation for adults | Expert consensus from the US sleep societies.[11] |
One of the gene variants behind it turns up in about 4 of every 100,000 people in a large gene database.[7] The odds that you are one of them are small.
“But I feel fine on 5 hours”
That feeling is the problem. In the lab study above, healthy adults were randomly given 4, 6 or 8 hours in bed every night for two weeks. Those with 6 hours or less kept getting worse on every test, until their deficits matched up to two nights without any sleep. Their own sleepiness ratings rose in the first days and then barely moved. The researchers concluded that they were largely unaware of how impaired they had become.[3]
That is why expert panels give a floor, not a range around your feelings: adults should sleep 7 hours or more on a regular basis.[11] How much you personally need may be more.
