There are several reasons why it is difficult to sleep: First, chronic lung disease, usually chronic bronchitis, chronic bronchial dilatation, chronic pulmonary heart disease or pulmonary hypertension leading to pulmonary insufficiency, especially during sleep. Second, heart failure, especially left heart failure as the significant clinical symptoms, left heart failure will appear when conscious sleep apnea, dyspnea, unable to lie down to breathe, sitting breathing and other clinical symptoms. Third, the brain cells are deprived of oxygen. When the partial pressure of oxygen in the arteries is insufficient, the partial pressure of carbon dioxide is too high, and the blood oxygen saturation is reduced, there will be abnormal ventilation and blood flow ratio, so there will be dizziness and difficulty in breathing during sleep. Fourth, if atherosclerotic heart disease, unstable angina, or myocardial ischemia caused by blockage of coronary arteries, there will also be symptoms of dyspnea after sleep.