What Causes Excessive Saliva With Choking At Night?

I am a 58 year old female. For about 4 months I have been having excessive salivation at night. I sleep on my back and have been choking in the night. It is severe at times. My hair and pillow are so wet that I have to change pillowcase in the night. I do not take any medications and have not had any health problems. My teeth are in good shape. I am very active. I am 5'5" and wt. 110 lbs. I have never had allergies or sinus problems.