When you are under extreme stress, you breath is more shallow and comes from your chest. When you are relaxed, you tend to breathe from your abdominal.
Before getting caught in a stressful situation, it is helpful to practice breathing deeply on a regular basis. Deep breathing is relaxing yet energizing. It helps calm the mind by focusing on the breath.
Intentionally paying attention to your breath on a regular basis will teach you how to have more control over your mind. You may think, “I just can’t stop my mind from going.” This may be true to a certain extent. However, if you build your skill of paying attention, you will find that you have more control over when to think and what to think than you previously thought.
Learn more about breathing here.