Hiatal hernia occurs when the upper part of the stomach moves up into the chest through a small opening in the diaphragm (a diaphragmatic hiatus). This is a common problem and most people are not bothered by it. A hernia may allow stomach acid to flow back into the esophagus (“food pipe”), where it can cause problems. The most common symptom is burning in your chest (heartburn), especially at night when you are lying down. Other possible signs include burping and trouble swallowing.