I just thought I'd post my experience as this forum really helped get me mentally prepared for my colonoscopy. I was told (wrongly) by my GP that at 31 I likely had bowel cancer. I had a colonoscopy and my doctor was incredible as were all of the support staff and nurses who looked after me. Who thought you could have a laugh in an operating theatre.

I cannot recommend enough for anyone thinking of having a colonoscopy without sedation to go for it. The procedure is not painful but there are a few moments of discomfort going round bends. The fact that you're fully conscious really helps because your brain is connecting the discomfort to the reason and most importantly you can see that it'll be over in seconds once the tube passes across the corners. I also had Entonox to hand in case I needed it. 
 

The procedure took just under ten minutes from camera in to camera out. I believe the doctor you have performing the procedure makes a massive difference, mine was absolutely faultless from start to finish. The benefit of no sedation was that I was in the car on the way to dinner within 25 minutes of the doctor finishing the procedure, at that stage people who'd been to theatre 40+ mins before me were still not fully roused and had hours to wait before they could go home.

One absolutely massive part of the discomfort was the buildup of gas inside the colon due to inflation being used to make it easier to pass the camera through... just fart, genuinely, just fart it takes the discomfort away instantly. Do not be embarrassed, if you try to hold onto that air you're quite literally causing your own discomfort. The doctors and nurses will not be bothered in the slightest and it'll make the whole thing go much easier. Focus purely on making the process as comfortable for you as possible, it's air and if it's outside of you it can't cause discomfort.

I know how frightening the whole process is, the thing it's likely being used to look for is frightening but, honestly, if you're reading this thinking 'should I, shouldn't I' then go for it, the worst that can happen is it gets too much and you can request sedation, but I guarantee you won't need it. You're in the hands of consummate professionals who are there to make you as comfortable as possible. Being awake you can watch in real time what's going on and the doctor can talk you through anything you see. 

This forum helped me an untold amount, if you're reading this thread you're doing the right thing. Go for it, you've got this!