What is indigestion and why is it so painful?

This week's question comes from Eunice O'Mahony in Toronto, who asked:

Can you tell me what exactly indigestion is, and why is it so painful?

According to Dr. Andrea Josse, a nutritional scientist at York University, indigestion is an uncomfortable feeling of fullness, pain, or burning in our gastrointestinal tract. There are many different causes of indigestion including simply eating too much or eating too fast, eating fatty foods or spicy foods that you're not used to, or consuming too much caffeine. It may also be a functional problem where you can't properly process certain foods like lactose.

Pain from indigestion can present itself in various ways. It often manifests as sharp or dull cramps and aches. Indigestion, specifically from increased stomach acid production, can trigger irritation and inflammation of the lining of the digestive system. Further down the digestive tract, distension of the stomach or intestines from excess gas production or too much food stretches the organs beyond the usual size, which also causes an uncomfortable feeling. In the bowels, excess water contributing to diarrhea can also cause pain until the contents are expelled from the body. 

Most episodes of indigestion are quick and go away within hours.