This condition is known as mouth breathing and it may lead to snoring also.Usually it might be due to nasal obstruction . If this condition is not rectified immediately it may lead to further complications.
Next Steps
Refer to ENT surgeon Or Maxillofacial prosthodontics.They might give you a splint to break your mouth breathing habit. or if there are nasal obstruction that can be corrected.
Health Tips
use a raised pillow while sleeping,use saline drops to clear nasal airway.Refer to your doctor if problems persists.