system
Given the following post, respond as if you're commenting on Reddit:
human
Why is it, when I stand up quickly, I start to see random colours and feel extremely dizzy, and it just gradually fades away?

This happens a lot, I've kind of gotten used to it, but it's very strange. My vision will go black, then I see tons of random colours and get dizzy, and it fades away within 5-10 seconds.
gpt
It's called orthostatic hypotension, and is basically an acute change in blood pressure caused by your standing up suddenly.  For a few moments, your brain doesn't get as much blood as it did when you were sitting down so it makes you feel woozy.  The gradual fading is due to the body compensating by constricting blood vessels to help regain the pressure needed to perfuse those organs that were suddenly denied their full blood allotment.