Sorry my memory isn't great these days, so I can't remember the name of the procedure I had (about 10 years ago), but he inserted a camera into my anus - they use lube - and just checked the last half of my "colon" (this is ridiculous I trained as a nurse and I did the digestive system as a speciality in one of my exams, I even explained part of the digestive system procedure on a different mumsnet topic a few months ago!) because with my symptoms I was passing bright red blood, if my stools had been darker than normal and it had turned out I was passing occult blood (occult only means "hidden" nothing spooky), then they would have checked my whole ..... ahhh ..guts (sorry the correct term just won't come to me), as it suggests that the blood loss could be coming from my small INTESTINES (Ilium? At least I remembered intestines at last!).
Anyway, I was, and am, too overweight to have sedation, so with a very nice nurse holding my hand the whole time, I had the procedure without any medication (except Diazepam that I got from my GP to relax me beforehand, as I was scared of having it without sedation). It didn't ever actually hurt (I suppose I compare everything to childbirth these days!), but it was uncomfortable at times, especially when he had to push it harder to go round the bends ☺ However, I was able to watch it on the same screen he was looking at, which was fascinating, and the nurse kept on talking to me about my children etc to keep me relaxed. If you can have Entonox then I would say go for it, I often used to say that I only had two more children so that I could have the Entonox!
If you are having your whole intestines checked then I really recommend having sedation as the small intestine has much tighter bends than the large, so that could make the procedure a bit harder.
My bigger worry for you would be the prep for the procedure. Do they want your bowels completely cleared, because although not painful, that prep is horrible. I can't remember if it took 2 or 3 days, but I had to drink this most disgusting stuff (presumably not as bad as in "I'm a celebrity", but still...). You obviously can't eat, and can only drink clear fluids eg no milk etc. I didn't want to eat anyway when having to force that stuff down me 😂 and of course, when it starts to work you need the loo quickly and often 😳 We don't have an ensuite, so my DH and I went to stay at a Premier Inn very near to the hospital - I didn't want an "accident" on the way to the hospital, and for that reason could not have used public transport, including a taxi, to get there.
So my big worry for you if you do have the procedure with sedation, and after not eating for several days, you could feel very faint afterwards, or even actually faint. So good luck OP, I am sure that the actual procedure itself will be fine. By the way, my outcome was that I hsd anal fissures that appeared to fill up my toilet bowl with bright red blood every so often, and weirdly after my procedure it has never happened again so far - about 10 years and counting...
Probably the best thing to do is ring your consultant's secretary, she will probably know all your options (even though she wouldn't normally be medically trained herself), and if she doesn't know then she can put you in contact with someone who does, occassionally that will be the consultant himself.
I have given the secretary a female pronoun, and the dr a male one just because that is what they were in my case, and I dislike using "they" unless really necessary..