There are many reasons for coughing in the second half of the night: First, the vagus nerve becomes excited in the second half of the night, and the excitement of the vagus nerve causes spasm of the bronchial smooth muscles, which can trigger coughing symptoms at this time. Second, the accumulation of phlegm in the lungs or bronchi and trachea during the latter part of the night can cause some irritation to the mucous membranes, which can also trigger the appearance of coughing symptoms. Third, because most people open their mouths to breathe at night, the air is dry without the nasal cavity, which can also cause the mucous membrane of the respiratory tract to dry out, and once the mucous membrane is dry, it can also trigger coughing symptoms.