Steven,
My anxiety attacks are daily, and can last for hours. But what ive noticed is that they peak. It comes on and gets progressively worse over a period of about half an hour, then seems to tail off somewhat. But because im having them so regularly now, it all seems to be rolling into one long anxiety attack, its horrible. Im taking Prozac which doesnt seem to be working that well (6 weeks into it now) and having CBT therapy which is early stages, so im struggling still, but hope to get over this one of these days
Go talk to the Doctor about whether your medication is correct.
Have you ever had anxiety/panic attacks that lasted for days? 
