Anal abscess forms in the anus or rectum when a cavity in the anal area gets filled with pus. This condition can cause severe pain, fatigue, fluid discharge, chill, and fever. In certain cases, the anal abscess can turn into a highly painful anal fistula. Fistulas generally happen when the abscess tears open on the skin surface. If an anal abscess does not heal by itself, then immediate surgical drainage of the abscess will be required.