The sympathetic nervous system or the "fight-or-flight response" is the preparation of the body to either run away from a threat or stand and fight a threat. This response starts in the autonomic system, where a physiological response makes the choice possible. This happens when adrenaline starts to flood the circulatory system, then the heart rate increases and the sweat glands become active. Next the lungs expand allowing for more air, pupils dilate, blood pressure increases and blood vessels dilate. This is the bodies response to the preparation of the "flight" portion of fight-or-flight. This is similar to a "panic attack", fear of heights or public
