system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 What exactly is your body doing during sleep to generate/recover energy for use the next day?

Bonus question, how is this energy stored?
gpt
Sleep is for your brain; it's not needed for the rest of your body and has nothing to do with physical energy

When you sleep, you brain clears itself out harmful toxins. The flow of cerebrospinal fluid in the brain increases dramatically, washing away harmful waste proteins that build up between brain cells during waking hours.

People who don't get enough sleep run an increased risk of getting Alzheimer's disease.