system
Given the following post, respond as if you're commenting on Reddit:
human
[ELI5] Why do I need to go to bed and sleep?
gpt
Think about yourself as a battery.  Throughout the day you use your charge, and sleep is your recharging period. This may seem odd because you'd assume that eating food and water would be able to keep your "battery" charged.  Well, when you sleep, your body just shuts down, and no longer has to focus on physical actions.  It basically takes this downtime to make sure the immune system is doing just fine and to let it recover after keeping you germ free for so long.

Why do you think doctors tell you to "stay in bed" when you're sick?  It's not because you feel like shit and therefore should not be walking around.  It's because sleeping helps your immune system get back on track.  Not sleeping leaves you more susceptible to disease and getting sick.

It's also important to sleep because your mind is reorganizing your thoughts from the day and days past.  

Why do you think people tell you to get a good night's sleep when you have a big test the next day?  

If you don't get a good sleep at night, say you stay up for 5 hours and get two hours of sleep after cramming for a test, you're not going to remember half of the things you crammed.  This is why teachers advise against cramming.  It's not because cramming is bad and doing it all in one night will overload your brain, its because the brain needs time to organize thoughts and ideas and learned information over night.

Think of your brain as a warehouse full of boxes and constantly getting new boxes. Every night little workers go in and organize the boxes, making sure you can find the information easily the next day.  The boxes are all different sizes.  Big boxes have big events in your past in them, like a traumatic experience.  Small boxes are things that didn't impact you or you didn't pay much attention to, like what you ate for dinner six months ago today.  As time goes on, these small boxes become of less interest to the brain and find their way in the back of the warehouse, gathering cobwebs (some people have brains that never do this, they're really cool and have photographic memories), while other boxes remain at the forefront.  If you don't get a good nights sleep, you're not going to remember much.

There are other reasons why you MUST sleep, and if you don't sleep you'll go crazy in two days and DIE in two weeks (I think that's the length).  Of course, your body will probably have forced you into sleep by then, so no worries.  

People that don't get enough sleep didn't have enough time to let their brain organize the boxes without more and more boxes flooding in (because we constantly take in new information during the day).  That's why they go crazy.  

So remember, get a good night's sleep!  It's very important.