What is stress?Stress causes your body to respond as though you are in danger. It creates hormones that speed up your heart, make you breathe faster, and give you a burst of energy. This is called the fight-or-flight stress response. Some stress is useful, but if it lasts too long it may cause headaches, an upset stomach, back pain, and trouble sleeping. It can weaken your immune system, making it harder to fight off disease. Fortunately, there are many ways to reduce your stress, including yoga, exercise, time management, laughter, and music