What is dysautonomia?

Dysautonomia is a category of disorders of the autonomic nervous system. For those unfamiliar with the ANS, it is the system that regulates all basic life functions in the body (think of it as the automatic part). It controls heart rate, blood pressure, body temperature, digestion, sleep, and a thousand other minute functions. The ANS has two branches, the sympathetic (think flight or fight) and the parasympathetic (like the great big off button in our brains). In my case, my disorder is characterized by excessive sympathetic response with some parasympathetic involvement.
As stimuli in sensed by the brain, be it physical or emotional, the hypothalamus and limbic system categorize that stimuli and order a response by the body. For example, the person is cold, and the brain recieves the message "cold", the ANS recognizes this sign, and tells the body to shiver. This is the appropriate response. In people with dysautonomia, the body may fail to recognize it, or my over respond. The person may then run a fever in response, or their body temperature may drop as no response occurs. The same thing happens with the heart rate and blood pressure. When we stand, the body does not get the message "standing" and fails to constrict the peripheral blood vessels to compensate. The blood pressure plummets, the heart rate increases (but again instead of increasing enough to compensate, it goes wildly high), and the person loses consciousness. Every basic function of the body is confused and inappropriate.
That is the most basic explination. In a later post I will describe the types of dysautonomias, including my own disorder, Hyperadrenegeric Postural Orthostatic Tachycardia Syndrome. This is complicated by Mast Cell Activation Disorder and Orthostatic Hypotension.