You know when it feels like your brain is mush and you're about to do this?
Well, there's actually a scientific reason behind it.
It's because, much like the garbage pale below, your cells are accumulating waste that needs to be excreted, as Distractify points out.
More specifically, the cells are building up that waste in the cerebrospinal fluid, or CSF. Not only does CSF act as a shock absorber, protecting your brain from banging against your skull, it also helps to transport metabolic waste, as explained by Britannica.
However, when you're awake, it 's difficult for your brain to excrete the excess build-up.
"You can think of it like having a house party. You can either entertain the guests or clean up the house, but you can't really do both at the same time," Dr. Maiken Nedergaard, a co-director of the University of Rochester Medical Center Center for Translational Neuromedicine, told TIME.
That is because when you sleep, your brain actually shrinks in size, "opening up the valleys for the CSF to circulate efficiently," as per Distractify.
Since we live in a dog-eat-dog world, there must be a very good reason why we spend so much time lying still, doing literally nothing. Well, there certainly is.
As stated by TIME from a study conducted by the URMC, "the brain's cells shrivel up by 60% while we sleep to wash away the cellular garbage more effectively."
So that's why it's so important to get a good night's sleep — and why you probably feel so sluggish on days when you don't rest enough the night before.
There is simply a ton of garbage in your brain that needs to get — in a way — thrown out.