I've never blacked out, but once I was riding with a friend back when SFA was Adventure World. We were on Python shuttle loop and after we went front ways through the loop she says, "I blacked out". Which instantly made me panic because we had about 4 seconds till we went through the loop backward. I didn't panic for me, I panicked for her, "We can't stop the ride now!" I think was my response for her.
Later, after she got her bearings for about an hour, we went to ride mind eraser and the same thing happened, so I told her we were going home (bummer).
Supersonic