Your diaphragm is a muscle that separates your chest from your abdomen and helps you to breathe. Normally, the diaphragm has an opening for the esophagus to pass through where it connects with the stomach.
At this point, the ring-like layer of muscle which acts as a one-way valve sometimes becomes lax.
When you have reflux disease, the weakened muscle allows the contents of your stomach to back up into your esophagus. This can cause considerable discomfort, often worse at night, with symptoms like heartburn, difficulty swallowing, chest pain and belching.
Reflux disease is often caused by a hiatal hernia, pregnancy, an ulcer or tumor of the esophagus. About half of the patients with severe Reflux Disease often have a hiatal hernia, which is a tear in the diaphragm.