Nighttime Revelation: Why Does Your Mouth Run While You Sleep?

Waking up with a wet pillow can be embarrassing, but drooling during sleep is often harmless. It can happen simply because of your sleeping position, an open mouth, or difficulty keeping saliva inside the mouth while deeply asleep. Side and stomach sleeping make drooling more likely because saliva can escape more easily with gravity. (Cleveland Clinic)

However, if drooling is new, excessive, or happening regularly, it may sometimes be connected to another issue that deserves attention.