system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why do people get sleepy from 2-5PM but wide awake from 2-5AM sometimes? Why isn’t it the opposite always?
gpt
When you eat, your body has to do work to digest the food. This is why you sometimes feel tired after lunch.

Most people don't eat in the middle of the night, so this isn't going to be a problem then, but when it's dark and quiet, lots of people get worried about things that they are too distracted to think about in the daytime, so they feel awake thinking about them because worry makes you alert to look out for danger.