system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How your body knows you slept enough and wakes you up?

Always wondered how that work.
gpt
It's pretty intuitive. Your body goes through cycles of sleep. You'll naturally sleep deeply for a while and lightly for a while. Sooner or later, you reach a point in a cycle where you're sleeping lightly enough that something is able to break through and disturb you - for instance, hunger, thirst, worry, pain, a full bladder, a sound. The more urgent the stimulus, the less deeply you have to be asleep for it to disturb you. If nothing pressing comes up you can sleep for a long time, but sooner or later your body will always need to eat, drink, pee, go to work, answer the phone, relieve pressure off your aching shoulder, find out where that damn car alarm is coming from, etc.