What if you never slept?

At night you get into bed. You close your eyes and fall asleep.

In the morning you wake up ready to play. What if you never went to sleep at all?

Every day ends the same way: you yawn, you get into bed, and you sleep. It can feel like a waste of time. You could be playing or reading instead!

So what if you never slept? Would you have more time for fun, or would something go wrong? We can't stop anyone from sleeping, and we wouldn't want to. But we can follow the clues scientists have found about what sleep does.

Humans spend roughly a third of their lives asleep. Yet the National Institute of Neurological Disorders and Stroke (NINDS) notes that the biological purpose of sleep remains a mystery.

This thought experiment asks what would change if sleep were removed. It follows three threads: what the brain does during sleep, how sleep relates to learning and memory, and how some animals manage with very little sleep or with half a brain asleep at a time. Each point is labeled as fact or idea.

Kids need lots of sleep. Most school kids need 9 to 12 hours every night.

While you sleep, your body rests and your brain keeps working.

You spend about one third of your time asleep. The CDC, the U.S. public health agency, says children aged 6 to 12 need 9 to 12 hours of sleep a night, and teenagers need 8 to 10 hours.

Sleep is not one long, still blank. Through the night you pass through different kinds of sleep again and again. In deep sleep your heartbeat and breathing slow right down. In REM sleep your eyes flick from side to side under your eyelids, and that is when most dreams happen.

NINDS describes two basic types of sleep: rapid eye movement (REM) and non-REM, which has three stages. Stage 1 is the brief changeover from waking; stage 2 is light sleep, where we spend most of the night; stage 3 is the deep sleep needed to feel refreshed. REM first appears about 90 minutes after falling asleep, with brain activity close to waking and most dreaming; we spend about two hours a night dreaming.

The CDC recommends 9 to 12 hours a day for ages 6 to 12 and 8 to 10 hours for ages 13 to 17. A homeostatic sleep drive grows stronger every hour we are awake.

Now pretend you never sleep. You would be awake all day and all night.

Scientists know that tired people find it hard to think and learn. Without any sleep, it might be very hard!

Scientists at NINDS explain that without sleep, your brain can't build and keep the pathways that let you learn and make new memories. Lack of sleep also makes it harder to concentrate and to react quickly. The National Heart, Lung, and Blood Institute adds that in children and teens, sleep supports growth and development.

So a world with no sleep might not give you more time for fun. You might struggle to remember what you learned, to focus on a game, or to get along with friends. Those are ideas built on real findings.

NINDS states that without sleep we cannot form or maintain the neural pathways that let us learn and create new memories, and that sleep loss impairs concentration and reaction time. It also calls quality sleep as essential to survival as food and water. The NHLBI adds that inadequate sleep over time affects how well people think, react, work, learn and get along with others, and raises the risk of chronic health problems.

Extrapolating to a person who never slept at all goes beyond any study, so those consequences are ideas. What the evidence does show is that sleep is not idle time: it is when the brain does work it cannot do as well while awake.

While you sleep, your brain sorts out what you learned today.

Scientists think it also tidies up, like cleaning your room!

Your brain stays very busy while you sleep. Scientists think sleep helps the brain sort the day's experiences into memories you can keep, and NINDS says both deep sleep and REM sleep are probably needed for this.

Recent studies also suggest sleep does housekeeping: it helps remove waste that builds up in the brain while you are awake. It's a bit like a cleaning crew that can only work when the building is closed. Scientists are still finding out exactly how all this works.

NINDS notes that sleep matters for how neurons communicate, that memory consolidation most likely requires both non-REM and REM sleep, and that recent findings suggest a housekeeping role in removing toxins that accumulate in the brain during waking. Sleep also affects almost every tissue and system, from the heart and lungs to metabolism and immune function.

Much is still open. Researchers continue to ask whether chronic sleep loss causes certain disorders or whether those disorders disturb sleep, and why sleep evolved at all. That uncertainty is exactly why a 'no sleep' world can only be explored as a thought experiment.

Some birds can sleep while they fly! Half of the brain sleeps while the other half stays awake.

Dolphins can do it too, so they can keep swimming.

Some animals have a clever trick. Scientists put tiny brain recorders on great frigatebirds, seabirds, and tracked them flying over the ocean for up to 10 days. They found that the birds can sleep while flying, sometimes with just one half of the brain asleep and the other half awake.

But the frigatebirds slept only about 41 minutes a day in the air, much less than on land. Dolphins also sleep with half the brain at a time and can keep swimming. Even these clever animals still sleep.

Rattenborg and colleagues (Nature Communications, 2016) recorded EEG from great frigatebirds flying over the ocean for up to 10 days. The birds slept in flight with either one hemisphere or both, mostly while circling in rising air, keeping the eye connected to the awake hemisphere facing the direction of flight. Yet they slept only 0.69 hours a day, 7.4 percent of their sleep time on land.

The same paper notes that dolphins use unihemispheric slow-wave sleep to monitor their surroundings and can swim during it. These animals reduce or divide sleep rather than abandon it, which supports the view that sleep serves functions animals cannot simply skip.