Exercise can help for anxiety disorders, such as panic disorder. Aerobic exercise, like walking, jogging, biking, or swimming, can help to reduce anxiety symtoms as an add-on treatment to other primary treatments, such as CBT (cognitive behavioral therapy) and prescription medication treatment. Exercise helps to release natural endorphins in your body, and helps you to feel better with less anxiety and nervousness.
However, exercise is not meant to be a primary treatment for panic disorder...you need other primary treatments such as CBT in order to treat it successfully.