The closest I've been to falling is when I clipped out coasting to a stop, then pedaled unclipped on top of the pedal. Of course, it silently clipped back in. I was falling past a 45 degree angle when I got the foot out. No fall, but I had a temporary muscle strain--ouch. I think this happened more than once.

That was a few years ago. Now it's second nature, I can clip in or out without having to think about it or plan how to handle a stop.