system
Given the following post, respond as if you're commenting on Reddit:
human
When I am falling asleep, why do I suddenly know that turning over will be more comfortable and can't sleep until I do?
gpt
These silly answers are way off. Fact is, your body has several systems (sinus, circulatory, etc) that alternate sides while you sleep to keep you turning over every so often to avoid tissue damage from prolonged weight on any certain part of your body.

Ever had a runny nose that kept switching nostrils? Same thing, same reason.