Gastroesophageal reflux disease (GERD)

A 60-year-old man comes to the emergency department because of sub-sternal chest pain for an hour. He has experienced this pain before, typically after heavy meals, during times of stress, and when he goes running in the park. He also feels the pain at night when he is lying in bed and has previously been woken from sleep by discomfort. He has not noticed any dyspnea, diaphoresis, or palpitations but is currently experiencing some nausea and a sour taste in his mouth. Medical history is non-contributory. ECG shows normal sinus rhythm. Which of the following is the most likely diagnosis?