I had this just over a month ago, it wasn't pleasant but the whole thing was over quickly. I'm not good with pain though so maybe it was worse for me than it would be for other people.
The whole thing was over in 15 ish minutes and I was fine afterwards (except for blurry vision of close up writing, which is a common side effect of something they gave me, that passed after 10 minutes or so).
I hope it goes well for you, I wouldn't worry as it is over so quick.
I've had a colonoscopy in September, air was pumped into my bowel but I didn't feel it at all. Only had a bit of wind at the end when it was over, with the air coming out...
I found it very easy, no pain at all, and it was over in less than 20 minutes. I didn't feel the air being pumped into the bowel. It didn't give me crumps, but some people say they felt like they had a mild tummy ache. I didn't.
The most difficult bit about the whole thing was the preparation: I was put on a limited diet for 2 days and after that had to drink 2 litres of a liquid that tasted of lemon, to make you go to the toilet and empty your bowels completely. After that you cannot eat anyhting for 24 hours before the exam. But you may not need this bit for your exam if it's done by scan.
So... relax. There's nothing to it. The nurses will explain everything when you get there and you can ask any questions. Alternatively you can ring Macmillan Trust as they are very good at explaining exams and procedures.
