I'm sorry but that product should never, ever be used on snakes. It contains over 2% PYRETHRINS which are very toxic to reptiles and fish and as you just found out, can cause severe neurological problems.

I don't know what a vet can necessarily do since there really isn't a treatment except supportive care - keep him in appropriate conditions and hope he works that crap out of his system.

In the future if you get mites use the tried-and-true treatments for snakes, either PAM or the NIX/RID mixed with water, always applied to the enclosure and never on the snake. Get some Natural Chemistry Reptile Spray for the snake.