I’ve just noticed, that when I take a nap, my body wakes myself up within 1 – 2 hours. This is probably true for everyone else too. But our bodies allow us to sleep for 8 hours at night. Why can’t our bodies nap for a full 8 hours without waking up? How does our body know this? How does our body differentiate between napping vs a nights sleep?
In: Biology
You should not take naps that long. Naps exceeding a hour can disrupt your sleeping at night. Then to your main question in order to sleep we use a thing called the circadian rhythms it is a clock in our brains that tells us when there is less light to sleep. Our ancestors needed to stay awake during the day so this clock helped them be attentive until it was necessary to sleep.
Think about how long it takes your phone to charge to full when you plug it in at empty versus at 60%.
Also think about how you’ll pull you phone off the charger when it’s got enough battery to get you to the next time you can charge it.
Same principles apply. Your body doesn’t need a full rest from empty, and it also doesn’t need to rest to full.
So you’ve never actually experienced the 5.5 hour nap that gives you a roulette wheel spin upon wakeup with the options: angry and confused, somehow more tired, wide awake for the next 16 hours leading to a crash, or (with a 1% chance) well rested? Automatic power naps sounds like a superpower, I wish I had that.
Your body has a rough sense of time that it uses to determine when to rest. For the most part it’s diurnal meaning we are awake during the day and sleep at night (the opposite of nocturnal like raccoons or bats).
This “internal clock” plays a part in telling us to go to sleep in the evening, but it’s not the only process that does so. Your brain also accumulates a sort of “brain waste” throughout your time awake, and mental exhaustion and sleepiness is your brain’s way of telling you it needs to flush that out. To us it seems like we are running out of energy like we’ve used up something, but really it’s that we need to flush something out. That’s why you can sleep extra to “catch up on sleep” but you can’t sleep extra ahead of time to “bank sleep” – you can’t empty any more waste past zero.
When you nap, you are letting your brain flush out some of its tiredness, but it doesn’t have as much to get rid of as after a full day, so that process doesn’t take as long. Then, when you’re only a little asleep and not in deep sleep because you don’t need it, that body clock says “oh wait, it’s daytime, shouldn’t you be awake?” And wakes you up.
So to EIL to start: Short naps only rest your body but not your brain. To get good “brain sleep” your body needs to rest for over an hour, and some people need 2 hours. Yor body is waiting to wake you until you get some solid “brain sleep”.
And adult explanation: Your body goes thru four stages during a sleep cycle. Only the last stage is the REM stage (Rapid Eye Movement) where you are actively dreaming. This stage is necessary for lots of brain things. We don’t fully understand them all but things like clear thinking and creating long-term memories won’t occur if you don’t get REM sleep.
The stages vary by person, but the first three take about 30 to 70 minutes to finish. Then the full REM stage will last from 15 to 60 minutes. So completing a full sleep cycle takes 1 to 2 hours (depending on your personal biology). So during your “day naps” your body is waking you up after it has competed a full sleep cycle. At night your body is completes the cycles multiple times, allowing you get to up for bathroom breaks or to roll over and steal the blanket from your partner between stages. This is important to know as five 20 little naps DO NOT equal an 80 minute sleep session. Use 20 min naps to relax your body. Use 1 to 2 hour naps to reset your brain and replace missed sleep at night (and maybe risk falling asleep 2 hours later tonight).
Wait – you can sleep for 8 hours straight at night?!?
Sometimes you can’t. I’ve had trouble sleeping for more than two hours at a time for many many years. An old friend of mine got like that too. I just take one or two two-hour naps a day. Plus due to a very long and involved story of being fucked over by the donation of a shitty bed by a very passive-aggressive friend of the family, my sister sprang one day for the best mattress in the store. She went into serious debt to pay for it. A queen-size Sealy Posturepedic pillow-top mattress. Meaning the entire top of the mattress is a pillow. I usually fall asleep within a minute’s time. Yesterday’s two hours’ sleep was a total power nap. I knew I wanted to keep working at the computer, but my eyes were crossing. So I just walked over in my clothes, laid down, knowing that a “minute” later it would be two hours, and then it was. Just like that. I sprang right back up and sat down again. Went back to what I was doing. After at least five years of every day being like this, my brain has adapted. I get heavy REM sleep during those couple of hours. According to an old psychiatrist, it can happen if you have long-term insomnia.
To actually answer your question and not just talk on a tangent, it’s actually very difficult to break out of the circadian cycle. People who work third shift have to learn to do it. When around people who aren’t night owls, you then remember that there are actually people who get sleepy at two a.m. Your body just wants to go into long-term downtime. You can offload the RAM and clear out your head with a nap, but usually you need to go through the long process of being asleep and not dreaming before the dreams start to kick in and you get the good REM.
It’s pretty much just our internal clock, it can be trained too if you set an alarm for say 20 minutes each time you nap after awhile you start to wake up 20 minutes after you fall asleep
All these answers are close but not on par…
You body has sleep and rest cycles. 20 Min and 90 Min
It’s easy to take a 20 min nap to refresh your body. Does not do much for the brain but helps the body relax. after 20 min your body wakes up easy and refreshed.
A 90 min nap is 1 natural sleep cycle, after 90 min you can wake refreshed in both mind and body.
This is why 7.5 to 8 hours sleep is best for most people, it’s 5 complete sleep cycles.
I have never in my life been able to take a 1 to 2 hour nap…
Sleep inertia is very real and my naps are usually 4 hours or more.
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