Hypersalivation, also known as sialorrhea or ptyalism, can trigger that as well. I had an episode of it after, of all things, an endoscopy. I saw two ENTs who couldn't help but my gastroenterologist did as he'd seen in patients with GERD. A few months of glycopyrrolate helped tame it down so I could sleep and it, eventually, went away.. If caused by excess saliva, the thinking is that the body's trying to dilute stomach acid. A condition called water brash in layman's terms. It was always worse when lying down and I used to get a sore throat from swallowing so frequently but the swallowing was to prevent choking feeling. (Note, not choking but a feeling that I'd have to. It was a sleep-destroyer and am glad that it finally waned.)