This might sound pretty obvious but sleeping on your back is a pose where all the saliva produced by your body stays in your mouth and doesn’t drool out. Conversely, if you sleep on your side or on your belly, the accumulated saliva will likely drip out of your mouth and on to the pillow.
If you feel it’s too difficult to stay in one position for the entire night, try tucking yourself in to stabilize your body.
3. Check for sleep apnea.