Dysautonomia literally means dysfunction of the autonomic nervous system. The
autonomic nervous system is the master regulator of all unconscious organ function throughout the body. It is involved in the control of heart rate, blood pressure, temperature, respiration, digestion and other vital functions. Dysfunction of the autonomic nervous system can produce the apparent malfunction of the organs it regulates. For this reason, dysautonomia patients often present with numerous, seemingly unrelated maladies.

Orthostatic intolerance is present when patients experience symptoms such as
lightheadedness, palpitations, and tremulousness during standing. Many patients also note other symptoms with upright posture: visual changes, discomfort in the head or neck, throbbing of the head, poor concentration, tiredness, weakness, and occasionally fainting. Patients can be severely impaired by these symptoms and signs, such as a bluish-red suffusion of skin in the lower extremities on standing, which are relieved by lying down

Often more simply referred to as postural tachycardia syndrome, or POTS, this disorder is characterized by the body's inability to make the necessary adjustments to counteract gravity when standing up. The defining symptom of POTS is an excessive heart rate increment upon standing. However, as you will discover, there are a multitude of other symptoms that often accompany this syndrome. As such, POTS can be a difficult disorder to detect and understand.

Sometimes referred to as neurally mediated syncope or vasovagal syncope, this disorder is characterized by an episodic fall in blood pressure and/or heart rate that results in fainting (Robertson, 2002).

A degenerative disease of the peripheral nervous system characterized by a marked  all in blood pressure upon standing (orthostatic hypotension). The orthostatic hypotension leads to symptoms associated with cerebral hypoperfusion, such as dizziness, fainting, visual disturbances and neck pain (Mathias, Mallipeddi & Bleasdale-Barr, 1999). Other symptoms such as chest pain, fatigue and sexual dysfunction may also occur. Symptoms are worse when standing and are sometimes relieved by sitting or lying flat.

References 1. Mathias, C. J., Mallipeddi, R. and Bleasdale-Barr, K. (1999). Symptoms associated with orthostatic hypotension in pure autonomic failure and multiple system  atrophy. Journal of Neurology, 246, (10), 893-898. 2. MEDLINEPlus Heath Information. (2003). Multiple System Atrophy. Retrieved September 8, 2003 from:
http://www.nlm.nih.gov/medlineplus/ency/article/000757.htm