system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 : How does our body know we are taking a nap instead of falling asleep for 8 hours?

When I take a nap I usually wake up after 2 hours without anything waking me up. How does my body know to wake me up?
gpt
This has a lot (but not everything) to do with how light it is. During the day the natural daylight prevents production of melatonin in the brain which is the hormone we produce that regulates our body clock and tells us when to go into a deep sleep. If it's not dark enough the brain won't produce enough of this hormone to go into deep sleep mode, hence the short naps - you never quite make it into the later stages of a big sleep.