Ahhh!! Yes, mine had a reaction to Advantix– exactly as you are describing. I don't know if my previous thread on it got erased, but I can't find it anymore on here.
My dog immediately started having issues with her back legs. She'd donkey kick for no reason-- and it was violent and it'd even scare her. We washed her with dish soap to get it off her coat/skin as much as we could. I did a google search for Advantix reactions and found a multitude of other owners who experienced the same issues-- some whose dogs never went back to normal!!
I have since sworn it off. Sorry... Ticks or not-- she's already shown she has a sensitivity to the product and I'm not taking any chances!!
I hope yours improve!! Keep us posted!