Mine have also been from sudden stops. They are the best. I mean when all of a sudden you go from 20 to ZERO miles an hour in less than 5 seconds. You are now at a full stop, and still clipped in, time to fall over... D'OH!!!
Forgot 1...
This hapened last week. Climbing a hill, I down shifted the chain fell off, and I just lost it. Over the side I went, at about 12 mph.... Laughed my @$$ off too. Cop pulls up, says he saw me fall, am I all right? I say yup, fell off, and just felt like laying here laughing for a few.