Nicole, I've seen horses that had EPM and recovered. So that's something that can be addressed (same stands for Lyme too BTW). :) The key is to diagnose it early enough and start the treatment.
And barrelbeginner, I understand it may sound very scary, however wait till you have vet out and he'll give his diagnosis, because all of us are just giving you different options (which is nothing but guessing). BTW, it also may be just arthritis (my horse developed couple months ago - scared me to death).
In any case keep us informed, please!