While I am scared of many of the above (falling on ice, crepey men in trucks, having the wrong time for races), I log many miles on a treadmill, and one of my greatest fears is tripping on my own feet or mis-stepping the moving belt, and falling on my face, in front of ALL OTHER MEMBERS OF THE GYM.This has happened, and it only makes my fear of it happening again worse. Luckily, this is probably the sole danger of treadmill running.