An interesting question, actually I ever experience like this
When you sleep with mouth opened, the saliva was increased and unknowingly dripping when you sleep. So avoid this habit as far as possible. Although it's not so easy, at least you can try to sleep with your mouth closed. If you have the same tendency to breathe through the mouth, applying different breathing exercises regularly throughout the day. They are almost simple yet effective way to treat this problem.
If the excess saliva production because of drug side effect, talk to your doctor imminently about it. If possible, the doctor will change the recipe to stop the drooling of saliva during sleep time and when you tend to sleep on side, try to lying back, this will reduce the possibility dripping from your mouth. Breathing through nose with mouth closed and sleep with lying is a useful ways for drool troubleshooting, drool when sleep not only causes shame problem when you sleep with others, but increase the risk of saliva fluid into the lungs.
If you do not succeed in treating the drool problem with your own care, do not hesitate to talk the doctor. Health experts will try to determine the factors that cause and suggest measures treatment to solve this. Inability to breathe through the nose usually derived from respiratory condition.
AEther*