A group of changes that occur in the body to help a person fight or take flight in stressful or dangerous situations. This is the body’s way of helping to protect itself from possible harm. During fight or flight, certain hormones, such as adrenaline and cortisol, are released into the blood. This causes an increase in blood pressure, heart rate, and breathing. Other changes include an increase in blood sugar, alertness, muscle tension, and sweating.