The occurrence of headache, fever, body aches, and weakness are all due to a series of changes caused by fever. A CT or MRI examination of the head is needed to rule out headaches caused by intracranial lesions. If there is no problem, it is caused by fever. Fever will cause the expansion of blood vessels in the head, and because of the increase in temperature, the intracranial pressure will rise, which will easily lead to the occurrence of headache. During fever, the amount of blood circulation throughout the body increases, and the relative lack of oxygen to the head occurs, which can also lead to headache symptoms. In addition, fever causes the body’s metabolic rate to increase, resulting in a large amount of anaerobic glycolysis and the production of excess lactic acid, which tends to accumulate in the muscles and cause pain all over the body. During fever, the consumption of energy, oxygen and physical energy is relatively high, so weakness may also occur.