Lying down to sleep feeling unable to breathe first of all to exclude obesity, and then consider the disease caused by diseases, such as respiratory system, cardiovascular system and other diseases caused. 1. Obesity: obesity will increase the burden on the heart and lungs, more fat to limit the thorax and diaphragm movement, causing the lungs to appear ventilation dysfunction, resulting in hypoxia, coupled with the heart enlargement, cardiac failure, which can lead to lying down to sleep when you feel out of breath. 2. Respiratory diseases: If the patient has a history of respiratory diseases, such as bronchial asthma, emphysema, cough variant asthma, etc., the sputum is not discharged smoothly after lying down, and the sputum is more blocking the respiratory tract, which causes chest tightness, breathlessness, coughing and other symptoms. In addition, lying down causes elevation of the diaphragm, further decline in lung function, dyspnea and so on. 3. Cardiovascular system diseases: such as chronic cardiac insufficiency, patients lie down after the increase in the amount of return blood, increasing the heart load, shortness of breath, chest tightness and other symptoms of gasping for air. Therefore, patients find that they can not breathe after lying down, it is recommended to go to the hospital for further examination to clarify the cause of the disease.