system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why am I wide awake at night after being exhausted all day/evening?
gpt
Because when youre very tired for a long period of time, and all you want to do is sleep all day, youre brain goes caveman mode and creates hormones that keep your body/brain going, because your brain (not your conscience/selfaware part of your brain.) thinks you wont be able to get sleep for a long time so it basically gives you lots of hormones that keep you awake, just like a hunter 4,000 years ago would stay up for days surviving, at first he would be tired, but after a while his body/brain would give him a burst of hormones/energy to keep you up, so you don't fall asleep in the middle of fending of a bear/lion/wolf/buffalo/unicorn.

TL;RD: Youre body gives you lots of hormones/energy when you have been up for a long time, to keep you up and alert.