system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do our eyes go black when we stand up after sitting for a while?
gpt
You're probably moving too fast. That's *orthostatic hypotension*, and that basically means your blood pressure to your brain dropped a lot from moving too fast. That's why you get dizzy and your vision goes blurry. Maybe try getting up a little more slowly in the future.