Dysautonomia is any disease or malfunction of the autonomic nervous system.
In some cases, dysautonomia results in a reduction in the ability of the heart and circulatory system to compensate for changes in posture, such as causing dizziness or fainting when standing or even sitting up. In other cases, inappropriate sinus tachycardia may cause the heart to race for no apparent reason. Other symptoms can include severe migraines, excessive urination.
Causes of dysautonomias are not fully understood, but they are thought to include viral illness, genetic factors, exposure to chemicals, pregnancy, autoimmune disorders, and a physical trauma or injury which damages the autonomic nervous system.[3]
There is no cure for dysautonomia, medications are used to stablize the condition on a long-term basis.
http://www.reference.com/browse/dysautonomia,+familial