Also called the fight-or-flight response, as identified by Dr. Walter B. Cannon of the Harvard Medical School almost one hundred years ago, it a profound set of involuntary physiological changes that occur whenever we are faced with a changing situation. This response, critical to the survival of primitive humankind, prepares the body for a physical reaction to a threat - to fight or flee. Confronted by this threat - physical or emotional, real or imagined - the hypothalamus causes the sympathetic nervous system to release epinephrine and norepinephrine (also known as adrenaline and noradrenaline) and other related hormones. When released into the body, these messengers propel you into a state of arousal.

When under stress:

	Your metabolism increases
	Your heart beats faster and your musclese tense
	Your breathing becomes shallow and you start to perspire
	The flow of blood to your internal organs and extremities decreases
	The fuctioning of your immune and digestive systems is inhibited

The stress response is useful and can be necessary in time of emergency, but the frequent or unrelenting triggering of the stress response in our modern life without a balancing relaxation response can contribute to a number of illnesses and symptoms.