Dysautonomia is an encompassing term used to describe any dysfunction of the Autonomic Nervous System (ANS), both Sympathetic and Parasympathetic divisions. The ANS is the part of the nervous system that regulates everything that happens in the body automatically, without cognitive thought, such as: respiration, swallowing, heart rate/blood pressure, dilation/constriction of pupils, organ function (including the stomach and intestines that work together for digestion), metabolism, temperature control (ability to sweat/shiver), the creation of bodily fluids (sweat, saliva and tears), the creation/release of chemicals and chemical reactions, sexual responses, etc. Dysautonomia is most common amongst those with damage done to the brainstem or Vagus Nerve.

Examples of Diagnoses of Dysautonomia include: Postural Orthostatic Tachycardia Syndrome (POTS), Neurocardiogenic Syncope (NCS) and Multiple System Atrophy (MSA).