Sudden fever overnight is commonly caused by some acute diseases, such as influenza, mostly caused by bacterial or viral infections when the body’s immune system is weakened, such as after a cold or exertion. In addition to common respiratory tract infections, many clinical diseases can cause sudden fever. For example, in acute urinary tract infections, in addition to fever, patients will have symptoms of frequent, urgent and painful urination. Patients with Streptococcus pneumoniae pneumonia may also present with sudden high fever. If the patient has a history of unclean sexual life, the fever of unknown origin must be taken seriously and can go for a sensory screening eight to exclude infectious diseases such as AIDS, syphilis, gonorrhea and hepatitis. If the patient has a clear history of unclean diet and fever accompanied by nausea, vomiting, watery stool and other manifestations, gastrointestinal infectious diseases such as bacterial dysentery or infectious diarrhea should be considered. Some chronic tumor patients may also develop high fever during the period of deterioration. In addition, some hematologic diseases, such as acute leukemia, may also present with sudden onset of hyperthermia. Sudden hyperthermia can also occur in response to clinical blood transfusions. When a fever develops, there are alternate fever-reducing medications and physical cooling options. If the fever is accompanied by other symptoms, such as diarrhea or coughing and wheezing, it is important to treat the cause promptly rather than blindly reducing the fever.