I just had a colonoscopy on Wednesday.
I had what's called "conscious sedation."
You have only a little nasal cannula (plain ole 02 in your nostrils!). No breathing tubes or other apparatus 'cause you are actually conscious.
They put an IV in your hand or arm. One tiny stick and that's it. If possible, ask for the combination of Demerol + Versed. It's a magical combination where despite being technically "awake," you have absolutely no awareness. I vow, you will be in la-la land! My recollection is that one minute I was trying to concentrate on finishing my sentences :-) and the next minute, my mom was standing there telling me they were all finished!
You do not have the worries of total sedation where you would need an anesthesiologist or anything because you are not "out cold." Yet from a discomfort point of view, there is NONE! I had no sensation of being even touched, "invaded," or anything like it! I wasn't even sore later, despite having a sessile polyp removed during the procedure.
I think you are being really smart to push for a colonoscopy instead of a sig scope. Why go through something twice? From what I've heard, you get little or no sedation with a sig scope, so a colonoscopy -- done right -- is actually EASIER! And so much better in every way. Good for you! Good luck, and don't worry!