I had to have a flexable sigmoidoscopy a few weeks ago for humira clinical trial I'm in . It was a very very painful experience. My body ended up shaking uncontrollably through the whole procedure due to the pain. They told me it wouldn't be a very painful even without sedation. Plus, I didn't want to have to find someone to come with me and drive me home so I I decided I didn't need the sedation. Luckily the procedure was only 3 or 4 minutes but it was a very unpleasant experience. I'm not trying to scare you. If you aren't flaring or are in a mild flare you probably don't need sedation. But if you are flaring, my flare is moderate with the lower colon pretty inflammed, and you don't get sedated you will be in a lot of pain. Even using the enema was a little difficult for me because my colon is so inflammed.
Honestly, I had a colonoscopy a few months early and was sedated. I would have much rather done that again, although the prep isn't nearly as bad for the flexable sig.
I guess the good news is, it is quick and will probably be painless if you aren't flaring or if you are sedated.