Complex sentence: A nutcracker esophagus refers to swallowing that can be extremely painful, and diffuse esophageal spasm refers to spasm of the esophagus that can be one cause of chest pain.
Split into simpler sentences: A nutcracker esophagus refers to swallowing that can be extremely painful. Diffuse esophageal spasm is a spasm of the esophagus that can be one cause of chest pain.