It was always my understanding that while sigmoidoscopies were often conducted without sedation, full colonoscopies never were. Perhaps i was mislead. I've had two, 5 years apart, just to check up on how things were. Both were done; but with different sedation each time.
The first was done with an intravenous opioid (I forget which, possibly diazepam), which was indeed interesting, since they allowed me to be awake during the parts that are less likely to be painful, and so i could watch the TV monitor and see what I look like (pink) on the inside, and follow their progress during the procedure. I also saw the tiny tiny yellow mushroom-shaped structures that were the earliest beginning of potential cancer tumors that were still at the earliest & most benign state (and were removed). That was the good part of this first procedure.
The bad part is that the doctor was in an excessive hurry because of his late start due to his incompetence in getting insurance company OK due to his faulty paperwork. He apparently made a tiny puncture in the left hand side of the transverse colon, just before it twists down & becomes the descending colon. This can potentially kill you, but because the puncture was very tiny, I didn't die, but had the 2nd worst fever of my life before the swelling sealed the puncture, and it started to heal. My temp got very close to the critical level for hospitalization & surgery, but never quite that high. The worst part was the interaction of the pain, fever & coming down from the diazepam (?), which caused intense nightmares, hallucinations, anxiety and inability to sleep much, which lasted for several days. My transverse colon felt like it was on fire. It was a colonoscopy from Hell. It remained so sore for the next 3 months, that i had to take daily enemas to prevent friction from material moving thru it. After that, no enema has ever felt erotic. My subconscious no longer associates one with anything other than potential danger & pain.
When the second one was scheduled 5 years later, I explained to the new doctor what had happened the first time. He suggested propofol to avoid this completely, since i would be unconscious throughout the procedure. I was OK with this because I had already had the scenic view earlier, and all that I would gain was a first hand confirmation that there was nothing wrong inside. I was willing to give up this personal confirmation to avoid any possible repeat of the prior experience. But things did not work out quite as they should that time either.
I was administered the propofol and told to lie quietly until it took effect. That's what I did, and they took my relaxed demeanor to indicate that I was fast asleep. But I WASN'T at all. Suddenly, the doctor rammed the instrument into me with one huge violent push, followed up immediately with another to get around the next bend. I think most patients have NO IDEA how VIOLENTLY this is done. I was completely unprepared for this, and the doctor was totally unprepared for my huge startled reaction and loud GASP. It was no fun, but now I know what they're really doing when you're knocked out.