Fight or Flight: The reaction that occurs in the body when faced by a sudden, unexpected threat or source of stress. The name of this reaction comes from the fact that an animal experiencing this reaction almost immediately decides to fight or to run. In this reaction there is a sudden release of the hormones epinephrine and norepinephrine, which increase blood flow to the muscles, increase arterial blood pressure, improve muscle strength and mental ability, as well as increase blood glucose Concentration. Through these actions the body prepares for a confrontation or a fast escape.