For example: If you normally sleep 7 hours per day and one day you only get 5 hours of sleep, chances are that the next day when you fall sleep you will sleep for around 9 hours. Or if you only sleep for a normal 7 hours that day you will still need more than 7 hours the day after that to feel fully rested.
How do brains keep track of how much sleep they lost and need to make up for?
In: 20
This is pretty much conjecture on my part, but my understanding is that a big function of sleep is to kinda flush and rebalance the chemicals in the brain.
So as long as the ratios are off, you’re still in “debt”.
How do you keep track of if the garbage is full?
Sleep does things for the body, things we don’t fully understand. One of those things is “tidying up” a bunch of blood chemicals and other things that accumulate over the waking hours. If it can’t clean all of them up, then you wake up with some already present. If those chemicals interfere with other things in a way that makes you “feel tired”, then guess what? You wake up tired.
It’s not that there are sensors in the body for all of these things, some of them are low-key toxic depending on how you want to define toxic. For example, some byproducts of exercise create chemicals that make it harder for your muscles to work hard. That’s part of why we get tired: the more those chemicals accumulate the harder it is for your muscles to do their job. So it really is like a trash can or dishes in the sink: if you let it pile up enough it starts to cause problems for unrelated things!
You “make up” for the sleep when you sleep enough to clear out all those things.
Your lymphatic system is like your body’s sewer system, carrying away your cell’s wastes to be broken down in your liver and then excreted in urine and stool. The lymphatic system doesn’t extend into your skull for lack of space. So instead, when you sleep, blood flow to your brain is reduced, causing blood vessels to contract slightly and allowing cerebrospinal fluid to flow between the blood vessel walls and your brain. This is when your brain cells dump the day’s saved-up wastes, which is mostly adenosine (your cells “burn” adenosine triphosphate for energy, and adenosine is the “ash” leftover), plus lipids and proteins from cellular repair.
When you feel sleepy, this is your brain detecting the build up of these wastes, which eventually begin interfering with normal functioning of your brain cells. When you don’t get enough sleep, not all of this waste has been removed, so today’s waste begins piling up on top of the remainder of yesterday’s waste, and you feel drowsy or groggy when normally you’d feel awake and alert.
Sleep schedules can be very precise things. I, for a weird fomo and also a lack of feeling tired when I don’t get much sleep, always have an alarm set for the same time every day. This has led to me being able to wake up if I forget to set my alarm, and wake up within <2 minutes of when my alarm is supposed to go off.
Your internal clock is very accurate, and if you usually get 7 hours of sleep a day, your brain will subconsciously keep track of that, as well as simply being more tired the next time you go to sleep.
It doesn’t. You can never really gain back damage you do if you’ve submitted yourself to significant periods of less-than-adequate sleep. But you can sleep well from here on out and prevent any more negative effects!
In addition to what everyone else has said about chemical “garbage disposal”, there’s also a need for down-time to tidy up thoughts.
It turns out that AI neutral networks also [get unstable without enough “sleep”](https://www.lifewire.com/why-artificial-intelligence-needs-to-sleep-5095871).
It’s a bit like how a supermarket spends time closed during working hours, not only for cleaning but also for internal organizing and tidying up that can’t be done while customers are around.
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