Why do fevers spike at night?

Answer 1

As you get tired, your immune system does to, thus sicknesses seem to worsen.

Answer:

Body temperature follows a circadian rhythm. This means it varies over the course of the day with a predictable period. There is a low around 6 a.m. and a peak about 12 hours later.

Observations indicate that this continues even when there is a fever. Therefore a fever peaks during the night.

There is also a consideration that the observations of increasing fever at night may be due to observation bias. People remember events that coincide with their expectations and forget those that contradict them (This is common in bingo players that "always win" when they have their lucky charms) The increases in night time fevers may be more common in anecdotal evidence than in statistical studies for this reason.

Answer 2

"Body temperature rises naturally in the evening, so a fever that was slight during the day can easily spike during sleep."

Answer 3

I don't know go some place else