It's uncomfortable but not painful really. I've had a few as I have celiac disease. Let's say that you don't have to worry about choking like with a gastroscopy, which I "luckily" had booked for the same day as the colonoscopy. I've never been sedated or had any anesthesia for either, it's really only the air afterwards that's painful, but that's not worse than when your stomach is upset during a flu or something.