Why You Drool in Your Sleep—and When to Worry? Drooling during sleep is common and usually harmless. It often happens during deep sleep when jaw muscles relax, causing the mouth to open and saliva to escape—especially if you sleep on your side or stomach.

Mouth breathing from nasal congestion (due to allergies or colds) can also increase drooling. In rare cases, it may signal health issues like sleep apnea, acid reflux, or neurological problems.

Occasional drooling is normal. But if it’s frequent, severe, or disrupts sleep, talk to a doctor. Changing sleep positions or treating congestion may help reduce it.