system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do you get dizzy if you stand up too fast?
gpt
So when you are sitting or laying down, your blood is sitting or laying down with you. When you get up really fast, your blood wants to be sitting or laying down still, so it is tired and moving slow. Your brain needs blood, but it takes a little bit for your blood to get back up from sitting or laying down.