I had the colonoscopy without anasthesia, it was over in 5 minutes with less pain than almost any visit to the dentist. The experience made me baffled at the insistence on total anasthesia, and the assumption the unanasthesized procedure is harrowing, that is often reported by people in private-insurance countries like the USA. So, I agree, if you need the procedure because of age or family history, just get it done.

I will say, the drink prescribed by my own GP tasted just fine, like any electrolyte sports drink in powdered form, so I think you were unlucky there!