Why does fever increase at night?
Normally, core body temperature is low in the morning and increases by few degree by the evening. So, a fever that was slight during the day can easliy spike by the night. Additionally, cortisol releases as a response to infection which is believed to be a protective mechanism against over activation of inflammatory system in the body. During night time, this protective mechanism is missed due to low cortisol levels and fever increases due to activation of inflammatory system.