In Sept, 2009, I developed micro-tears in one of my Achilles tendons and wound up in a walking boot for something like 6 weeks. The cause was never really determined, but it seemed likely a combination of the side-effect of an antibiotic that was known for such things and pushing it much too hard in the treadmill (that was when I was first trying to exercise).

It isn't pleasant, for sure. All they could do for me was to put me in a walking boot and wait for it to heal...I am afraid that I don't have anything very helpful to say but I do hope that you are feeling better!