Out of breath generally refers to dyspnea, a lie down feel dyspnea should be alert to the occurrence of a number of diseases, such as heart failure, bronchial asthma, mediastinal tumors, etc., should be promptly consulted to identify the cause of the disease. 1, heart failure: due to myocardial tension or contraction dysfunction, cardiac output is not enough to maintain the metabolic needs of the organization and the disease, the patient usually lie down when the symptoms of dyspnea, need to sit and breathe to relieve the symptoms, but also can be accompanied by physical activity limitations and so on. 2, bronchial asthma: the main symptom of the patient for recurrent episodes of wheezing, can be accompanied by shortness of breath, chest tightness, cough, etc., mostly associated with exposure to allergens, cold air, exercise, etc., often in the night and early morning episodes or aggravation. Severe bronchial asthma can be short of breath at rest, difficulty in breathing when lying down, need to sit and breathe, severe asthma attack can also lead to respiratory failure. 3, mediastinal tumor: If there is a mediastinal tumor, due to gravity, the mediastinal tumor compresses the trachea or lung tissue after the patient lies down, resulting in poor breathing, usually accompanied by chest pain, dry cough and other symptoms. In addition, pregnant women due to uterine enlargement compression of lung tissue can also appear when lying down dyspnea, this symptom can also be seen in chronic obstructive pulmonary disease, lung cancer, pleural effusion and other patients, should consult the doctor in a timely manner, improve the relevant examination, a clear diagnosis, and the doctor to carry out the appropriate treatment.