Gastroesophageal reflux disease (GERD) is a common cause. Conditions that inflame the food pipe cause heartburn, nausea, and indigestion. Symptoms often intensify when lying down.
Gastritis is when the stomach walls become irritated and inflamed. This can lead to a sense of pain or burning, as well as nausea, vomiting, and gas. Untreated cases can lead to ulcers, bleeding, and cancer.