Hi
Welcome to the MedHelp forum!
There is a possibility is that you have a seizure attack and suffer from sleep apnea. This again can be diagnosed by a combination of EEG and sleep studies. You will need to consult a sleep specialist and a neurologist. Until you are seen by a specialist and the treatment started and effective, please sleep on a mattress on the floor. Take care!
According to my doctor and according to what I've read, you're actually feeling your blood pressure bottom out. Except your brain can't tell you that, so it provides you with a sensation or image to explain the feeling!
When I was a kid I thought it was God rocking me to sleep. As an adult I always jerk completely awake because I imagine myself tripping or falling. It's irritating as all get it, and it usually only occurs when I am falling asleep fast. And it happens nearly every night!
No clue how to stop it, except maybe to drink more water.