I've had panic disorder since I was 5. I know the feeling your talking about and even though I'm now 23, I still don't know how to get rid of it. I don't know if you've heard of Lucinda Bassett but I would highly recommend looking into her program. Anyway I was listening to one of her CDs about anxiety and she talked about this feeling and said its your body's way of giving itself a break. She was saying that this feeling is a good thing. I hate feeling that way but you just have to know its a normal response to anxiety. It might take some time but the feeling always goes away.
That's been the worst symptom for my anxiety, but unfortunately, I have no advice on how to help it. :(