Colonoscopies are not that bad; many countries do it without sedation. The sedation part is annoying in multiple ways; it prevents you from doing a bunch of stuff the rest of the day, while without sedation, you can continue as if not much has happened afterward.

Even endoscopies are possible without sedation, but most people don't have the ability to not squirm or gag for that one. You can even see youtube videos of people doing that one without sedation.