I had a flexible sigmoidoscopy about 3 years ago -- it's not quite as invasive as
a colonoscopy, but the tubing still goes pretty far.  The prep wasn't pleasant,
but it wasn't THAT bad -- it was a HELL of a lot less painful than the REASON I
had to have it done in the first place, which turned out to be inconclusive (and
the problem went away entirely once I started low-carbing).  What's unexpected
and disconcerting is probably AFTERWARD as you walk away, worried about leakage
and trying (in vain) not to emit sloppy wet farts (Robin Williams did a GREAT
routine on that in his last HBO special).  They pump gas into you during the
procedure to expand things, and it's got to go SOMEWHERE.  One of the WORST parts
was that everyone waiting for a colonoscopy or sigmoidoscopy at the clinic during
the next hour had to wait in a teeny, tiny waiting room that was smaller than
some family dinner tables I've seen!  So there we all were, about 9 of us, all
cramped into this little room with our knees practically touching those of the
person ACROSS from us, all KNOWING what we were all there for and trying not only
to not look at each other, but to not even acknowledge anyone else's EXISTENCE.  
Bring reading material, even if you don't know how to read :-)  

LOL

I get frequent bouts of diarrhoea, and was talking medical stuff with a
friend who has had the same problem recently, and she gave me an excellent
tip: use baby wipes!

It seems so simple, but I would never have thought of it!

cheers
Rachel
(New Zealand)

just remember that if they find anything with the "virtual" they will have
to go in with the regular... (and they usually do find polyps).. so be
prepared to undergo the regular one too..