Fell off of my bike twice this summer... but I fell on opposite sides to maintain balance in the universe. Anyway, the first time I did it I was in a pace line behind 4 other people and was trying to avoid hitting the dude in front of me by staring at him. except staring made me go closer. I hit him at 25 mph+.
Second time I was going uphill and my gears locked up so I went over the handlebars...