Indigestion, also known as dyspepsia or upset stomach, is a condition of impaired digestion. Symptoms may include upper abdominal fullness, heartburn, nausea, belching, flatulence or upper abdominal pain. People may also experience feeling full earlier than expected when eating. Indigestion is relatively common, affecting 20% of people at some point during their life, and is frequently caused by gastroesophageal reflux disease (GERD) or gastritis.