If a patient has a fever in the second half of the night, it may be due to the following major types of diseases: 1. The most common factor is infectious, such as when the body is infected by bacteria, viruses, fungi or other atypical microorganisms, such as mycoplasma or chlamydia. And the body temperature has a circadian pattern to follow, and the fever due to infection is especially obvious in the latter half of the night, so the most common factor for fever in the latter half of the night is infectious disease.2. Fever in the latter half of the night can also occur in some connective tissue diseases and immune system diseases, such as patients with systemic lupus erythematosus, dermatomyositis, and dry syndrome, and this condition also causes fever in the latter half of the night, but with a low fever type, mainly. 3. If endocrine system diseases occur, such as hyperthyroidism or hyperadrenocorticism, fever may also occur in the second half of the night.