Is colitis dangerous even without symptoms being present? i experienced bloody stool for about a month several years ago but no symptoms since.

Colitis is dangerous: Colitis means "inflammation of the colon" & can be caused by infection, ischemia (poor blood flow), inflammatory bowel disease (ulcerative colitis, crohn's), mechanical trauma (chemical burns), post-operative (diversion colitis), etc. Inflammation that extends thru the full thickness of the colon (transmural colitis) is most dangerous & places the patient at significant risk, depending on cause.