system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is that when we experience a blow to the head we “see stars”?
gpt
that's shock, which can result in a rapid lowering of blood pressure, so as to mitigate bleeding out if you were injured. 

that lowering of blood pressure can make you pass out, or see stars, or essentially feel dazed. It also might have to do with brain injury if the blow was bad enough.