system
Given the following post, respond as if you're commenting on Reddit:
human
Why do people become more awake after a certain point in the night?

I've talked it over with a few people, and everyone's agreed that there's a certain time of night (it varies between people) after which people aren't really tired and become more awake and aware again. After that point, it's much harder to get to sleep. Why does this happen?
gpt
You have two systems that drive you to sleep (1) the homeostatic system that tallies your sleep debt and (2) the circadian system that makes sure you sleep at the right time by regulating both sleep drive and arousal (making sure you stay awake). If you wait long enough during the night the circadian drive to put you to sleep will lighten up and it will begin to promote wakefulness. The problem is that eventually your sleep debt will mount and you won't be able to stay awake during the day even if your circadian system is promoting arousal.