Sympathetic storming is excessive uncontrolled activation of a sympathetic nerve system. The sympathetic nerve system is responsible for the control of body arousal which includes heart rate, respiration, perspiration, release of adrenaline, and other characteristics that your body gives off in response to stress.
Sympathetic storms are a common complication of a traumatic brain injury and tend to cause increased elevated body temperatures or increased heart rates or perspiration. At the same time it can also do exactly the opposite and lower your heart rate or induce your adrenaline. So it can work in both directions and it’s a very common complication of a traumatic brain injury.