Stomach trouble is a general term used to describe a variety of digestive issues, such as indigestion, nausea, and abdominal pain. Two common causes of stomach trouble are knots and ulcers. A KNOT is a localized area of tension or tightness in the muscles of the abdomen, while an ULCER is an open sore that develops on the lining of the stomach or small intestine. Both can cause severe discomfort and can be treated with medication or lifestyle changes.