The colonoscopy isn't as bad as you'd think. I had mine at 40 and they put me to sleep using a mild anesthetic, and I was waking up in the recovery soon after without feeling a thing.
As a bonus, I got to keep some high res photos of the inside of my intestines - that's worth the ride.
The worst thing about it for me was drinking that awful laxative solution the night before to clean out my system. That was tough because you have to drink 8 oz. every 10 minutes until it's all gone. It sounds easy, but after about 6 glasses that 10 minutes arrives way too fast. Once you get it all down though - get ready to turn on the fire hose!
