Stress is what you feel when you have to handle more than you are used to. When you are stressed, your body responds as though you are in danger. It makes 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 normal and even useful. Stress can help if you need to work hard or react quickly. For example, it can help you win a race or finish an important job on time.