I had one last year. The worst part is having to drink that gallon of drek they give you to clean you out. The procedure itself was nothing, since my doctor puts you out for it. But I have to say, I could only get about a fourth of the liquid down you have to drink before hand and when I got to the office I told them thinking it wouldn't be enough, but it was (maybe because I'm on the petite side at 5' 2" and 108 pounds) and they did the procedure as planned. Made me very glad I didn't force down (even if I could have) the other three fourths of that drink!:D
Good luck with your procedure!