A colonoscopy is sometimes recommended to investigate for polyps or other anamolies in the large intestines.
I had a colonoscopy done about 2 years ago. You will be given some stuff to consume the night before to ensure you empty your bowels. Otherwise, the surgeon's view will kenah blocked.
I opted for no sedative for quick recovery. The sedative does not guarantee a painless procedure, but it helps to make the patient less nervous. And you will need to remain in the recovery area until you are assessed to be well enough to leave the place. The scope is stiff as it is fibre optic, and there will be some resistance when turning round the corners.
The discomfort of going through the procedure without sedative will depend on individual pain tolerance levels. For me, it was bearable, and it meant that I was able to leave the place within 15mins of completion.