I have mild ulcerative colitis, today i had a sudden onset of severe abdominal pain/bloating, nasea and bright red blood should i go to er?

Yes: Ulcerative colitis is a chronic disease of the colon, in which the lining becomes inflamed and develops tiny ulcers. Uc is the result of an abnormal response by your body's immune system by sending white blood cells into the lining of the intestines, where they produce chronic inflammation and ulcerations. Uc can cause abdominal discomfort and frequent bowel movements and occasionally bleeding.