system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Why do some injuries hurt at the moment of impact while others hurt the day after?

 For example let's say you fall and you can't move for a a few seconds because your knee really hurts, peter griffin style, but the next day what really hurts is like your back or your shoulders. Why is the pain at that moment so sudden and goes away quickly while the other will come a while after?
gpt
There are two types of pain:

* an immediate severe one to make you escape closest danger (e. g. you'll reflexively remove your hand from a flame or a sharp object);

* afterwards a different, long-lasting, deep ache if you have been seriously hurt. Its function seems to be to send you (or any animal) into a safe place to heal, and also to limit exercise while getting better.