system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Got a bad cold, runny nose. Why does it stop running when I'm asleep?
gpt
Most likely if actually doesn't - it doesn't run out our noses. Our sinuses drain out our nostrils when standing or sitting because of gravity. This means we have to blow or wipe our nose. When sleeping lying on your back or side the mucus will drain into your throat - again because of gravity.

This is one of the biggest reasons many people wake up coughing when sick - clearing their throat of mucus. The mucus, by the way, is produced as a part of the body's immune response to kill off the cold virus.

Feel better soon!