If by “your mouth runs” you mean drooling while you sleep, it’s usually because saliva continues to be produced while the muscles that keep it in your mouth relax during sleep.
Common reasons
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Sleeping on your side or stomach makes it easier for saliva to escape.
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Mouth breathing from nasal congestion, allergies, a cold, or a blocked nose.
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Acid reflux, which can sometimes increase saliva production.
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Sleep apnea, especially if you also snore loudly, gasp, choke during sleep, or feel excessively tired during the day.
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Certain medications can increase saliva production or affect swallowing.
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Less commonly, neurological conditions can cause excessive drooling, particularly when accompanied by difficulty swallowing or other neurological symptoms.
Occasional drooling is usually harmless. If it becomes new, excessive, or persistent, or you develop difficulty swallowing, choking, facial weakness, or speech changes, get medical advice.
A simple first step is to address nasal congestion and make sure you’re getting adequate, comfortable sleep.
