I suffer from Chronic Fatigue Syndrome as a result of my brain injury. While the precise mechanisms of CFS are still a matter of debate by the medical community (and unfortunately in many cases, its very existence), in my view is a disorder characterized by inappropriate immune system symptoms.

For example, I have myalgia, constant muscle pain. Myalgia is an appropriate response if one has a flu, for example, in that it discourages excessive movement of the organism, inducing it to rest and recover.

With certain types of brain injury, there is loss or impairment of a very important stage of the immune response- the signal to turn it back off. The I.S. becomes a runaway, sapping off tremendous amounts of metabolic energy, and producing the titular "fatigue" of chronic fatigue.

Your chills are very similar to the myalgia I experience. You have gotten chills from an actual flu in the past, yes? Chills and shivering is a way of generating body heat in an attempt to kill the infection. Something has triggered them now, and your body is not getting the "off" signal it needs.

This is analogous to the anger issues some of us experience. Anger is a basic survival emotion generated deep in the limbic area of the brain, and is mainly regulated by the frontal cerebral lobes. In a frontal damage victim, emotional impulse control is compromized, and the anger is acted out.