My very first experience w/a scope was an upper endoscopy followed by a colonoscopy, same day one right after the other. Sedated, you are no more aware of one than the other.
HOWEVER, a double balloon endoscopy is NOT the same thing as a "normal" or "regular" upper endoscopy followed by a colonoscopy.
Its been awhile since I ready about the double balloon endoscopy, it was right after they were approved in the US.
As I remember it, they start a scope at one end and continue on thru as close to half of the small intestine as possible. That area is marked. Then they start a scope at the other end and continue on thru as close to half of the small intestine as possible. Ideally they meet at the mark or beyond so that they observe the entire GI tract from mouth to anus. The scope is "assisted" by little suction cup type "thingies" that crawl thru the GI tract like little catterpillar feet. The intestines, both large and small, are "ribbed" like slinkys. The little catterpillar feet close the "slinky" up pulling it back tighter rather than looser like a loosened slinky and that is how they are able to observe all or most all of the intestines.
Try a google or PubMed search on double balloon endoscopy.