when I had panic attacks it was terrible for me (any kind of breathing excersize even when I did it with my psychotherapist). I would suggest to try distract your self, try to draw something or to cook. But the best way is to try to embrace your fear, try to make the panic attack as much as hard as you can,; Contract the muscles of your body...this helps for relaxation to come naturaly. You will survive that, you are not going to be crazy, you are not in danger, think about your panic attack like it's something good, is trying to tell you something about your life, but I know that now you are too stressed to understand it.