system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does stuffy nose go away briefly after standing up?
gpt
One of the things that makes up a stuffy nose is the mucus membranes being inflamed.  They are literally puffed up with blood.  
   
When you stand up suddenly, your blood pressure in your head drops for a bit.  That's the reason why some people get a bit light-headed when they jump up.  And that drop in blood pressure briefly helps the membranes in your nose go back towards normal.