Scott - it's weird that he was getting so much better - and maybe he associates you with medication time. This is horrible if he IS, because you have done all you can to get him better - and it did work for a while.
I think a second opinion is a good idea. Also, someone on Pet Talk has mentioned a psychic who is inexpensive and has worked wonders for people here.
She apparently charges about $30 and can be paid after - it's the animals she wants to help.
I don't think you have anything to lose. I'll PM the person who has the info (moosmom?)
HUGS - don't give up yet!
"You can say any foolish thing to a dog, and the dog will give you a look that says, 'Wow, you're right! I never would've thought of that!'" -- Dave Barry