A bad gut feeling is a term used to describe a feeling of unease or anxiety in the stomach. It is often associated with physical symptoms such as nausea, indigestion, and heartburn. Two common medical conditions that can cause a bad gut feeling are AGITA and ULCER. AGITA is an Italian word for heartburn, indigestion, or stomach pain. An ULCER is an open sore in the lining of the stomach or intestine. Both of these conditions can cause a person to experience a bad gut feeling.