Waking up with a wet pillow every once in a while is usually nothing to worry about. Drooling during sleep is common because the muscles involved in swallowing relax, and saliva can escape when you sleep with your mouth open.
However, if you suddenly begin drooling much more than usual—or it happens almost every night—it may be worth paying attention to the possible reason.
Here are six conditions that can sometimes be associated with excessive nighttime drooling.