Part of the problem is your anxiety disorder, and part of it is the fact that you don't get any exercise at all. Your heart is a muscle, and it too needs exercise. So it gets weak and when you perform some physical activity, it has to work harder. I suggest that once a day you get up and walk around the block. Nothing terribly strenuous, just a little walk. The point is to do it every day. You will gradually get stronger, and then you can extend the walk. This is the most effective and least dangerous way to start to strengthen your heart and body. Get treatment for your anxiety disorder. It's interfering with your life.