Fever is a result of activators in the body, such as viruses, bacteria, and allergens, which stimulate the immune system. The inflammatory factors secreted by the immune system cause a rise in the thermoregulatory point in the brain, which increases heat production and decreases heat dissipation, resulting in an increase in body temperature, so fever is a result rather than a cause. Inflammatory factors also stimulate the brain center, causing sympathetic excitation, which increases the heart rate and speeds up blood circulation, which increases the amount of blood entering the brain. The brain is a space enclosed by the skull and has a limited capacity, so when the blood increases to a certain level, the pressure in the brain will rise, causing headaches. The arteries in the brain itself have a regulatory function, that is, they have a certain degree of elasticity, but when the blood entering the brain increases, the arteries will contract violently to reduce the blood flow into the brain and prevent the pressure in the brain from continuing to rise. The process of arterial contraction is felt because it is larger than usual, and simply put, it is a jumping sensation.