What causes the hot and cold spells when you have the flu?

One minute I'm sweating my * off, the next I'm shivering under 3 blankets. How come?
Answers:
When you are feverish, your internal thermostat has been re- set, to help you fight infection. This explains it well, IMO:http://www.merck.com/mmhe/sec17/ch188/ch."FeverBody temperature increases (fever) as a protective response to infection and injury. The elevated body temperature enhances the body's defense mechanisms, although it can cause discomfort for the person. Temperature is considered elevated when it is higher than 100掳 F as measured by an oral thermometer. Although 98.6掳 F is considered "normal" temperature, body temperature varies throughout the day, being lowest in the early morning and highest in the late afternoon鈥攕ometimes reaching 99.9掳 F.A part of the brain called the hypothalamus controls body temperature. Fever results from an actual resetting of the hypothalamus's thermostat. The body raises its temperature to a higher level by moving (shunting) blood from the skin surface to the interior of the body, thus reducing heat loss. Shivering (chills) may occur to increase heat production through muscle contraction. The body's efforts to conserve and produce heat continue until blood reaches the hypothalamus at the new, higher temperature. The new, higher temperature is then maintained. Later, when the thermostat is reset to its normal level, the body eliminates excess heat through sweating and shunting of blood to the skin.Fever may follow a pattern: sometimes temperature peaks every day and then returns to normal. Alternatively, fever may be remittent, in which the temperature varies but does not return to normal. Certain people (for example, alcoholics, the very old, and the very young) may experience a drop in temperature as a response to severe infection.Substances that cause fever are called pyrogens. Pyrogens can come from inside or outside the body. Microorganisms and the substances they produce (such as toxins) are examples of pyrogens formed outside the body. Pyrogens formed inside the body are usually produced by monocytes. Pyrogens from outside the body cause fever by stimulating the body to release its own pyrogens. However, infection is not the sole cause of fever; fever also may result from inflammation, cancer, or an allergic reaction.{I omit a section aimed at doctors, here.}.Because fever helps the body defend against infection, there is some debate as to whether it should be routinely treated. However, a person with a high fever generally feels much better when the fever is treated.Drugs used to lower body temperature are called antipyretics. The most effective and widely used antipyretics are acetaminophenSome Trade Names
TYLENOL
and the nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirinSome Trade Names
ECOTRIN
ASPERGUM
and ibuprofenSome Trade Names
ADVIL
MOTRIN
NUPRIN
. However, aspirinSome Trade Names
ECOTRIN
ASPERGUM
should not be given to children and teenagers to treat a fever because it increases the risk of Reye's syndrome (see What Is Reye's Syndrome?), which can be fatal.

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Because your running a temperature.

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This is science. When you are running a fever/flu, your body temperature is so much higher than the temperature outside. Heat tries to leave your body. You feel hot because you are like a heat emitter. But after some time your body finds a way to repond to the heat and generate perspiration and sweat which oozes out of your pores on the skin.This is when you experience coolness because the perspiration evaporates off your skin, giving you a cold sensation, which sometimes sends a chill down your body. You don't need a lot of perspiration just to experience that. as long as evaporation takes place, you'll feel it.So the process follows a cycle and you'll feel cold after hot and hot after cold.

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