I had to do it last May to prep for abdominal surgery, and almost didn't make it, but I did. It was really awful, and for months afterward my stomach would curl at the thought. I know your pain!
I'm supposed to have a colonoscopy, too, but I can't bear the thought of going through that again. Someone was telling me that there's something in pill form they can give now. A couple people I've talked to about it said it works great, but another person (maybe she works in a doc's office?) said it tends not to work as well for some people.
I'm going to ask for it, though!