system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does my body know when I've had enough sleep and it's time to wake up?
gpt
It's hard to answer that because with today's knowledge we can't really explain why we need sleep, aside from the fact that we feel tired.  Not knowing why we get to sleep in the first place, it's hard to say why we stop sleeping.  To our knowledge the best answer would be: because we stop feeling tired.