Most cases of fever when sleeping occur because the body’s thermoregulation is weakened during sleep. The body’s thermoregulatory effect decreases, and once the disease causing the fever occurs, the thermoregulatory center of the brain is not able to play its thermoregulatory role, and the body temperature rises. There are many reasons for this, first of all, it is common to have a fever caused by a cold virus infection or a bacterial infection. This is because when bacteria or viruses grow and multiply in the body, they produce a lot of toxins that constantly stimulate the body’s thermoregulatory center. When sleeping at night, the role of the thermoregulatory center is significantly weakened and the fever may appear, so that the fever appears as soon as you go to sleep. It is still necessary to choose the appropriate antibiotics or antiviral drugs for anti-inflammatory treatment depending on the type of infection. If the temperature of the fever is high, more than 38.5 degrees, you also need to use antipyretic drugs for treatment, such as acetaminophen. Secondly, non-infectious factors can also cause fever as soon as you go to sleep, such as malignant tumors or diseases of the rheumatic immune system.