Severe sympathetic overactivity occurs in several conditions that are recognized as medical emergencies. Following central nervous system injury, a small proportion of individuals develop severe paroxysmal sympathetic and motor overactivity. These individuals have a high attendant risk of unnecessary secondary morbidity. Following acquired brain injury, the syndrome is known by a number of names including dysautonomia and sympathetic storm. Dysautonomia is currently a diagnosis of exclusion and often goes unrecognized. The evidence base for management is almost entirely anecdotal in nature; there has been little structured or prospective research. In contrast, the evidence base for autonomic dysreflexia following spinal cord injury is much stronger, with level 1 evidence for many treatment interventions. This review presents a current understanding of each condition and suggests simple management protocols. With the marked disparity in the literature for the two conditions, the main focus is on the literature for dysautonomia. The similarity between these two conditions and the other autonomic emergency conditions is discussed.