In human context, stress is any pressure or demand (mental or physical) faced by you. It is your body’s physical and psychological response to danger or anything you perceive as overwhelming. When stress is overcome, relaxation ensues.
Your body responds to sudden danger or emotional shock by flooding the bloodstream with adrenaline and hormones that get you ready for action. Muscles tense, blood-sugar levels increase, and your heart rate and blood pressure rise. These surges could help save your life in a dangerous situation.