It seems like most people have had good results with no issues with that product. I know that some products can make a snake lethargic but Im not seeing this being one of them.

Were the mites really bad? Could they have zapped the life from the snake? Any other changes in the setup or conditions?

BTW, you can bring mites home from pet shops, shows, or any place that has them. They can hitch hike home with you. Many people shed their clothes once they get back from such a place and make sure they and their body is washed before entering their snake area.