I had my 1st last year and it was fine, I didn't have to drink anything beforehand and I chose not to have sedation. I was taken into a room with a bed & loo in it, the nurse put liquid in my bum & told me to wait 10 mins. At 1st it was ok, but after 7 mins I dashed to the loo!
I found it not too bad, the biggest thing I felt was my rectum was stretched, as it is briefly for a big poo, I had to remind myself not to push it out.
I could see on the tv that my large intestine was ok, the screen was right near me. The staff were great, chatty & nice and it was ok. I would do the same again if I needed to, and probably I will cos I seem to be getting all sorts of weird conditions. Good luck, I'm sure you'll find it not as bad as you imagine