Drooling during sleep is often a sign that your body is deeply relaxed and experiencing good quality rest. It happens mainly during deep or REM sleep, when muscle activity slows down, including swallowing. This relaxation allows saliva to escape more easily without being swallowed.
Sleepin position plays a big role in drooling. Those who sleep on their side or stomach are more prone to drooling because gravity pulls saliva out of the mouth. On the other hand, people who sleep on their backs tend to swallow saliva more effectively, reducing drool.