It is very common to have a bad cough at 4:00 or 5:00 am. Whether it is a respiratory infection or an asthma-induced cough, it is easy to have a bad cough at 4:00 or 5:00 am. This is because the vagus nerve is easily excited in the early morning or at night, which can lead to spasm of the bronchial smooth muscle and contraction of the bronchi or trachea, resulting in a strong cough. In addition, when people sleep at night, most of them breathe with their mouths open and the dry air enters the respiratory tract directly through the mouth without being moistened by the nasal cavity. coughing.