I agree with the previous poster that yoga twice a day is probably too much, even if you're already in shape. Could you be having some kind of allergic reaction that's causing your symptoms? It could be something as simple as the cleaning products they use at the yoga studio, or anything else that's different than what you're normally exposed to. If you're having chest pain, that's something you'd want to get checked out by your doctor right away, especially if it continues.
"You may have a fresh start any moment you choose, for this thing that we call "failure" is not the falling down but the staying down." Mary Pickford
"No matter how slow you go, you are still lapping everybody on the couch."