Coughing while lying down and not coughing while sitting up may be due to bronchitis, it may also be due to gastroesophageal reflux disease (GERD), and it may also be due to pulmonary stasis caused by left heart failure. 1. Bronchitis: When bronchitis occurs in a patient, the inflammation leads to an increase in local secretions, and these secretions can irritate the throat leading to coughing symptoms. If the patient’s sputum is relatively small, the symptom that the patient coughs when lying down and does not cough when sitting up will occur. 2. Gastroesophageal Reflux Disease (GERD): GERD patients are prone to reflux of gastric contents because the stomach is at the same level as the esophagus and the pharynx when they are lying down. If the reflux reaches the pharynx, it can cause the patient to have an irritating cough, whereas when sitting up, it is not easy to have reflux and therefore no cough. 3. Left heart failure: Patients with left heart failure are prone to pulmonary stasis and may cough up pink foamy sputum. This symptom becomes obvious when the patient lies down and the amount of blood returning to the heart increases. When sitting up, the symptoms of pulmonary stasis are relieved because blood accumulates in the sagging lower limb area. Therefore, patients with left heart failure may experience symptoms of coughing when lying down and not coughing when sitting up. In addition to the above diseases, other diseases can also cause patients to cough when lying down and not cough when sitting up.