fight-or-flight response fight-or-flight response the fight-or-flight or the fight-flight-or-freeze-fawn (also called hyperarousal or the acute stress response) is a physiological reaction that occurs in response to a perceived harmful event, attack, or threat to survival. it was first described by walter bradford cannon. his theory states that animals react to threats with a general discharge of the sympathetic nervous system, preparing the animal for fighting or fleeing. more specifically, the adrenal medulla produces a hormonal cascade that results in the secretion of catecholamines, especially norepinephrine and epinephrine. the hormones estrogen, testosterone, and cortisol, as well as the neurotransmitters dopamine and serotonin, also affect how organisms react to stress. the hormone osteocalcin might also play a part. a dog and cat expressing the fight (top) and flight (bottom) response simultaneously. this response is recognised as the first stage of the general adaptation syndrome that regulates stress responses among vertebrates and other organisms. name originally understood as the fight-or-flight response in cannon's research, the state of hyperarousal results in several responses beyond fighting or fleeing. this has led people to calling it the fight, flight, freeze response (or fight-flight-faint-or-freeze, among other variants). the wider array of responses, such as freezing, fainting, fleeing, or experiencing fright, has led researchers to use more neutral or accommodating terminology such as hyperarousal or the acute stress response. physiology autonomic nervous system