Ok, this isn't going to be much help, but maybe you can do a little more research on it.
I was watching "Mystery Diagnosis" like a week ago and there was a story about a girl who had almost the exact same thing, except she slept right through it. She'd cough, sit up, vomit, and go back to sleep.
Unfortunately (and this is where I'm not of much help) I fell asleep before I found out what the cause it.
BUT apparently stuff like this happens. Talk to you MD, or get a referral to a gastroenterologist. Don't give up! Someone will be able to help you out!