During the ALARM STAGEĀ of the general adaptation syndrome, catecholamines are released by the adrenal medulla, intense arousal occurs, and the body mobilizes internal physical resources to meet the demands of the stress-producing event.
This gives the body a burst of energy to flee from the scene that causes the stress to prevent the further damage that might happen to the body. Kind of similar when you accidentally touch the flame on a candle, your body automatically undergoes alarm stage and signals your brain to move your hand away from the heat that caused you pain.