system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why do we need to sleep?

why do we get tired and are there animals that don't sleep?

I find this is quite a strange behaviour. We eat to get energy. We breathe to get oxygen. We sleep to… well… to what? Why can our body not do what it does while we're awake? Instead we put ourselves on a bed in a dedicated room, cuddle and then pass out for a few hours – totally defenseless.
gpt
The nervous system removes various waste products during sleep. 

For that to happen the glial cells contract and expand.

They cant do that while you are awake, well maybe they could but it would probably not go very well since they handle a substantial amount of cognition during your waking hours too.
Hence you have to sleep so that your body can carry out the trash.

Like a big frivolous party where the cleaning ladies have to wait for the party to end before they start cleaning.