The only ongoing pain I would have is an aching, heaviness pain, like cramps but in a different place. Then I might have blinding pain in my lower gut during bowel movements when I am flaring.
Also, my alergy to sulfa manifested itself in a slight rash on my arms, that's all. Did you tell your doctor about it?
That's my experience. I've never had toxic colon but my impression is also that if you have it you won't be going at all, and it would be very clear something is wrong.
Asacol and Lialda are good maintenance meds, but they might not work very well to get you out of a worsening flare. That's why we end up on predisone. At 20/day, you probably should ask your doctor about other meds, either prednisone or rectal meds.
I don't think you need to go the hospital or ER (a miserable place), but trust your instincts.
49 year old female attorney, diagnosed UC/pancolitis 1985, no surgery but much suffering. Asacol/5ASA 6x400 mg maintenance for 20+ years; use prednisone & Rowasa for flares.
August 2008 sought care of naturopathic doctor. Food sensitivity test showed wheat/gluten, other intolerances; eliminated wheat/gluten from my diet. Probiotics (Ultimate Flora, 50 billion).
Bad flare in March, seasonal? Back on prednisone, 40-30-25-20-15... Humira denied, started Remicade 4/12.