Why sleep?

Apparently not doing it will kill you. And your not alone, every living animal specie on earth must sleep to stay alive. Why?

Obviously science has ideas but no conclusive proof or really any idea why, so what do you think? Is sleep the reason for existence? Does sleep somehow connect the mind with the soul? Or is sleep more of an evolutionary product that every specie was somehow forced to develop for survival?

Might be a function of our planet, day night cycles and the eco-niche each species occupies, better to sleep during inopportune times then stay awake. Also seasonal patterns such as hibernation seems to agree with it’s a function of the planet.

This is all going off memory of things I’ve read over the years.

When you sleep, your neurons shrink a bit and this makes it far easier for CSF to flood your brain and wash out all the waste products built up over the day. I think the rate of these things being washed out goes up by 20x when you are asleep vs awake. Sleep also helps your body repair itself. So your body repairs itself, and the waste products in your brain get washed out. So it is a necessary function at minimum due to these 2 things, there are probably other benefits.

There are people who need very little sleep. They are just genetically built to only need 2-4 hours a night of sleep. Those people seemingly have no negative effects from this condition. I forget what it is called, but people can function fine on 2-4 hours an night of sleep, assuming that is all your body thinks it needs. If your body thinks it needs 7-8 like most people, but you try to only get 2-4, you will have serious side effects.

Other than fatal familial insomnia, I don’t think insomnia will actually kill you. The studies showing sleep deprivation leads to death were done on rats, which may not apply to humans. Other than FFI or accidents caused by insomnia, insomnia itself is not fatal.

Neuroscience is still in its infancy, we have only been studying it in earned for a few decades. So there are many unanswered questions.

The amount of sleep needed varies drastically by animal. Some animals sleep 2 hours a day, some sleep 20. No idea why.

(Bolding mine) The singular of “species” is “species”, not “specie”. FYI.

My head “thinks” it wants 7-8 hours, but the truth is that I’m just as tired after 7-8 hours of sleep as I am after 4-5 hours of sleep–so I just sleep 4-5, because I really can use the extra time. I realize this could have serious side effects, but I’ve been doing it so long now I can’t really stay asleep mucho longer anyway.

Thank you, Needscoffee.

Another data point, speaking from personal experience: Going several days in a row without sufficient sleep is enough to drive at least some people literally insane. (Full disclosure: I’m bipolar manic/depressive.)

I think that’s the point. The question shouldn’t be “Why do we sleep?” but “Why can’t we not sleep?”

I think that’s the answer science can’t figure out. They may know of all the benefits and activities sleep provides, but not why we have to be unconscious for them to happen. i.e. why don’t they occur when we’re in a meditative state, or just relaxing?


Based on my own experience, while I am not a doctor, it is likely you have a sleep disorder, such as sleep apnea. If I don’t breathe well when I sleep, I don’t sleep well and wake up as tired as when I went to sleep. Sleep apnea has serious medical consequences. By not sleeping long enough or well enough, I’m putting extra stress on my heart every single day. I have a family history of heart problems, so this is very dangerous for me over the long term. I advise you to talk to your doctor, or to a sleep specialist. And look for threads on the SDMB about CPAP machines (continuous positive air pressure - forces air into the nose and/or mouth to keep the passages open so I can breathe effectively when I sleep.)

This also addresses the question of why sleep matters - if you don’t you could have a heart attack. IMO, sleep is so deeply ingrained in our bodies that we cannot do without it. No matter how much fun it would be to do your favorite activity 24x7 forever.

Why do we sleep? It’s the only time 99.999% of males get to have sex with a supermodel.

Spelled correctly or not, the statement is not true. Most “higher forms” of animals seem to require some sort of sleep, but not so for more primitive forms.

At best,iIt might be more accurate to say “we don’t know”, because sleep becomes more difficult to define when we look at very primitive animal species.


I’m also as tired after 8 hours of sleep as after 5, even after other issues are dealt with (restless legs, apnea). Testing suggests I have “Excessive Daytime Sleepiness” which is doctor-ese for “shrug - you’re just tireder than other people. Here, take these pills if you want to function”.

“These pills” being Nuvigil or Provigil. If I’ve had adequate quantity of sleep, they make the difference between very very tired and merely low energy. If I haven’t had adequate quantity, they make the the difference between stumbling-into-walls and tired-but-functional.

In any case, what you describe suggests to me that you may well have some kind of undiagnosed sleep / wake disorder.

I will NOT do any significant driving (i.e. trip driving - I’m fine for running errands etc.) without the meds on board now. I do often skip the meds on weekends or other days where I can get by with being brain-dead.

Which part is it more accurate to say “we don’t know”? Are you saying your answer is “we don’t know”? And also how difficult is it to define sleep? What primitive animals are you having trouble defining as sleeping?

Im really asking for an opinionated answer on the act of sleeping but if you want to get technical on what defines sleep in the animal kingdom, I would sure listen.

Sleep seems to play an important role in brain function. If people are prevented from sleeping they become psychotic. Just a few days of no sleep and most people start hallucinating and suffer quite severe deficits in cognitive functioning. People who have sleep disorders in their 50s develop dementia at much higher rates in their 60s and 70s.

I personally suspect sleep started out in evolution as just a way to conserve energy and save lives-if you are a night-foraging animal that is at high risk of being nabbed by predators during daylight, it’s a good strategy to lie motionless all day, and why not kind of turn things off while you do that? And then as the brain developed further, it piggy-backed on the downtime (as evolution often does) to perform some kind of cleaning/repair work during the downtime.

It seems that only mammals and birds sleep as we define sleep, with specific brain-wave patterns indicated periods of REM sleep. Reptiles, amphibians, fish, and bugs may go into periods of motionlessness and torpor but I don’t think they are “sleeping” precisely as we define it, based on EEG measurements. Interestingly, birds can sleep one half of the brain at a time.

I should have clarified that I really was talking about how I felt upon waking. After getting up, swimming (2kms), and going to work, I’m fine. The afternoon is fine, too, providing I can sleep about 20 minutes about mid-day.

What I really should have said is that the whole 8 hours don’t make a such a big difference on the whole. The 20-minute siesta at mid-day seems to me as helpful as three additional hours at night.

However, you could be right, in that I could just be functioning at below level and not even knowing it.

It can also trigger depression, not as serious as what you are describing, but disruptive nonetheless.

The term is “short sleeper”. They sleep much less than normal people, without the unpleasant and unhealthy effects that someone who is just not getting enough sleep has. In fact they tend to be unusually alert and energetic as I recall.

Even dolphins and similar aquatic mammals sleep, but they do so only one brain hemisphere at a time as they must be somewhat active to breathe.

On the contrary, sleep deprivation actually improves symptoms of depression: