Dysautonomia is any disease or malfunction of the autonomic nervous system. This includes postural orthostatic tachycardia syndrome (POTS) , neurocardiogenic syncope, mitral valve prolapse dysautonomia, pure autonomic failure, multiple system atrophy (Shy-Drager syndrome), and a number of lesser-known disorders.

In some cases dysautonomia results in a reduction in the ability of the heart and circulatory system to compensate for changes in posture, causing dizziness or syncope (fainting) when one, eg, stands suddenly. In other cases, the heart may race (tachycardia) for no apparent reason, or the kidneys may fail to properly retain water (diabetes insipidus).

The effects of dysautonomia may be minor, only limiting the patient's activities slightly, or they may be totally disabling, leaving the patient bedridden. Chronic fatigue syndrome is often associated with dysautonomia.