I has this problem also. I would wake up with my stomach so distended it looked like I was pregnant with twins. It hurt so bad and I had tachycardia episodes with this. I called my MD and he lowered my bi pap from 21 to 16. I have not had any major episodes like that again. I do have "farts" now but not the stomach distention. My boys now have something to tease me about when they slip out!   Good luck!

Kathi, I do think you are swallowing air and I don't think you have to open your mouth to do it.  Anyway, some months ago, someone made a suggestion about the cause that at least sounds plausible, lacking any kind of study on the subject.  If your mouth gets dry during the night, you may be swallowing so you can distribute your saliva around your mouth and in the process you also swallow air.  I certainly don't know how to go about proving that and, unfortunately, I don't know how to stop it or why it happens to some people and not others.  Maybe more humidity would help?