Sedation always carries some risk, and you should be fully informed. Sometimes you have to look out for yourself.
You may also want to recognize that analgesics -- pain killers -- are not the same as amnesics -- "sedation" -- so demanding to be highly sedated may not effect the pain you feel, just your memory of it. Being pain free is not mutually exclusive to being fully conscious.
Hopefully, any office using propofol has a CRNA bedside.
You can't stay on pred forever. The drug protocol doesn't vary much, and if you're already using rectal meds with an ASA and pred, the next step is likely immunosuppressants or anti-TNF agents -- whether you have a colonoscopy or not.
Good luck.