Stress: Body, Mind, Emotion, and Behavior
Stress is your emotional and physiological response to a perceived threat, real or imagined. When "stressed out" you may experience increased heart rate and breathing, muscle tension, dilated pupils, and a rush of adrenaline preparing you for "fight or flight."
What is important to understand is that most of our daily stress results from our perception, which we have the ability to control; do we choose to feel threatened or are we up for the challenge? Modifications to your perception go a long way in the amelioration of stress.