I thought I would post because before I had this procedure I searched for experiences of people who'd had it without sedation and couldn't find any. I had the procedure this morning and I opted to forego the sedative because no one was available to collect me afterwards. So if you're considering this option it may be useful for you to hear about my experience.
First of all, I wasn't actually that nervous about the colonoscopy, I was dreading the 24 hours of no food beforehand, plus the laxatives. Both were not as bad as expected. The hunger wasn't too bad and the longer you go without food, the easier it is to bear. When my blood sugar got low I just had sugary black tea or lucozade and I was fine as long as I didn't do much activity. The laxatives weren't too awful, but as someone else suggested I recommend using baby wipes instead of toilet paper as you will be much less sore. I think I probably went to the toilet about 10 or 12 times in total, it wasn't nice but not horrendous either.
Now for the colonoscopy. Ok, it's not pleasant but you wouldn't expect it to be. It's uncomfortable having something in your bottom for that length of time (about 20 mins), and it does make you feel like you want to go to the toilet. The discomfort of the scope going through your bowel is bearable, the only bits where I winced slightly were when it was 'going round the corners'. At those points it feels like trapped wind (not painful as such, but I get a sort of urgency feeling, and can feel my stomach expanding). But the doctor apologised when he could see my discomfort and he was as careful as possible, maybe more so because I hadn't been sedated.
At times you can feel the tube moving around inside which is a bit weird. And sometimes the doctor sort of pulls it out slightly before pshing it forward again, which is uncomfortable because again it makes you feel you need to go to the loo. I tried not to think about it too much, or to prevent anything happening because it's less uncomfortable if you're not clenching. I didn't feel embarrassed because the medical staff do this all the time and you're never going to see them again anyway!
Afterwards I was passing quite a lot of air because they pump air in while they're doing it. I think they also put water in a couple of times, so you might find you need to go to the loo afterwards.
The best thing about not having the sedative is that you can eat straight away (finally!), and then go home. No waiting around or feeling groggy. So if you are unable to have sedation for whatever reason, don't worry too much. Whatever you feel you would have felt anyway, it's just that you have to use other methods to relax, like focussing on something in the room, deep breathing, talking to the nurses etc.
Do check with your doctor beforehand that they will let you have it without, because the last thing you want is to do the fasting and have the bowel prep, only to get there and find they won't do it because you have to have sedation and there's no one to collect you. Hope this helps someone.