I had an awful reaction a few years ago with the prep before my colonoscopy,i did not pass out,but i was on the floor,nauseated,vomiting,dizzy could not move as i was so weak,and the Diahorrea was horrendous.My husband had to lift me of the bathroom floor as i was to weak to move.He phoned the hospital and they told me to stop taking the prep and to still come for my examination the next day which i did although i was feeling ill.The doctor was very shocked when i told him the state i was in and he actually said he felt guilty about it,but there really was not much else he could say or do.I have never taken any prep since and i do not think i could i would be terrified!