system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does my severely blocked and streaming nose clear up on its own simply by standing up?

I currently have the cold and notice my nose feels completely blocked when lying or sitting down but it seems to clear as soon as I stand up, what's going on?
gpt
Most of the blocked up feeling isn't due to mucus, it's down to your sinuses being inflamed and swollen with blood. When sitting or lying down, the relative blood pressure in your face is higher and they swell more, making you feel more bunged up. When you stand up your heart has to pump blood higher (and expend more power pumping more blood back to itself from your feet) so the blood pressure in your face drops and your sinus meats become less swollen widening your airways and making your nose feel clearer even though you're still dealing with the same amount of snot.