Hello Sub,
In the past I have had exactly what you are describing...actually several times and I knew when it happened that it was anxiety. I remember sipping water and my hand shaking so bad I was spilling it. I felt cold and then got the shivers, I even remember it feeling like my back was almost spazzing like, as I was shaking and I also remember it kind of wearing me out...tired. I think for me it lasted about 20 minutes as well.
As far as the breathing...if you are producing adrenaline as we typically do during an attack, it tends to tighten the chest...just remember to breath from your stomach at all times...not your chest. As you learn what coping skills work best for you...like breathing from your diaphragm...as you begin to relax, the breathing should be less of an effort.
Best advice I can give it learn to roll with whatever symptoms you have. You can't ignore it but just breath and do your best to stay calm....the chemical release will end much quicker if you don't try to fight how you feel...distract yourself or just go about your business, paying as little attention to the anxiety and the episodes will shorten....Best wishes....WM