I had a similar experience. I was taking [brand name sleeping pill] for insomnia. After an hour or so of sleep, I wound up in a funny position where I could neither breathe nor wake up completely. With modern sleeping pills, you move in mysterious ways. After 20-30 seconds of panic I was able to thrash myself into a position where I could get my lungs pumping again. There's a mocking remark above this one about not being able to breathe not being scary enough to be in this thread. Which is nonsense, of course. When you can't breathe, autonomic responses take over and your body is in hyper-panic mode. That's the secret to the effectiveness of water-boarding.
Wow. I wonder if our experiences count as being scary enough?