Dysautonomia (or autonomic dysfunction) is any disease or malfunction of the autonomic nervous system (ANS). The autonomic nervous system controls a number of functions in the body, such as heart rate, blood pressure, digestive tract peristalsis, and sweating, amongst others. Dysfunction of the ANS can involve any of these functions.
A number of conditions are forms of dysautonomia: postural orthostatic tachycardia syndrome (POTS), inappropriate sinus tachycardia (IST), vasovagal syncope, pure autonomic failure, neurocardiogenic syncope (NCS), neurally mediated hypotension (NMH), orthostatic hypotension, orthostatic hypertension, autonomic instability, paroxysmal sympathetic hyperactivity, and a number of lesser-known disorders such as cerebral salt-wasting syndrome and mitral valve prolapse syndrome (different from mitral valve prolapse). Dysautonomia may occur as the result of other diseases, such as diabetes mellitus, multiple system atrophy (Shy-Drager syndrome), Guillain-Barré syndrome, Lyme disease, or Ehlers-Danlos syndrome, along with a number of other conditions that may affect the nervous system.