Lawdy, I haven't heard of "mask sedation" in years and years and years, if ever, for a scope!!!!
Most certianly I would be discussing this matter w/your doctor NOW, well before scope time!!! Is this the same doctor? Same facility? Do NOT rely on them to remember your previous experience!!!!
I most certainly DO discuss sedation w/my gastro before my scopes! I prefer w/o any sedation most times. If I have to have sedation for any reason for my colonoscopy I prefer and ask for Propofol (diprivan). Not all facilities can offer Propofol. Two of our local facilities can, a third facility (my favorite, naturally) can not offer Propofol.
There is no reversal agent for Propofol so most states REQUIRE an anesthesiologist for its administration AND full life support availability which MOST doctor's offices can NOT provide.