Build up of saliva at night, anyone else?

Hi everyone,

I've had this issue where I've had alot of saliva build up whenever I sleep, to the point where I drool excessively. This only happens when I'm sleeping and often when I nap (usually if its longer than an hour) and sorry for the grossness - but its SO MUCH. Like I wake up and spit out a mouthful of saliva every morning without fail, regardless of whether I have brushed and flossed or not, This is not an issue during the day and only happens at night. I've asked doctors and dentists and no one has any idea on what this is, what its caused by or anything. Any advice would be super helpful as its embarrassing, disgusting and negatively affects my sleep due to the excessive drooling.