I too have been choking while asleep with excessive saliva. I could also be awake when my secretion glands go haywire, but never knew the cause. I am a smoker too, no acid reflux or sleep apnea, and have recently experienced chest pains and pains in my left arm. I went to a cardiologist who diagnosed me with diastolic dysfunction which can cause a back up of fluids in the lungs. Not saying that this is the cause, but you may want to get that checked out as well. Since my diagnosis and treatment, I have not had a problem with excessive saliva and choking. I have also started taking meds for smoking cessation.
I have something similar but only when I lay on my right side. Do you lay on your side, stomach, or back? Until this gets resolved, I would lay on you side if you are concerned about choking.