Reflux

Some people have a condition called gastrosesophageal reflux disease (GERD) that causes stomach acid to move backward up into the esophagus. This produces the uncomfortable, burning sensation we call heartburn. The symptoms of GERD can be worse when a person is lying down. So even if the person doesn't notice the feelings of heartburn because he or she is sleeping, the discomfort it causes can still interfere with the sleep cycle.