I personally think that anyone who runs a fitness class should be trained in first aid and prepared to deal with seizures...if that is not the case I would be a little worried about taking a class there. Do they know CPR? What if something worse happens? If you want to continue going I would pull them aside and tell them about your condition, what needs to happen, and maybe even provide a pamphlet or instruction sheet that they can keep.
See if you can tell the group before or after the class. You might want to bring someone with you that knows about your condition.
You go to a Zumba class? Wow, are you gullible. You pay for old music you probably already have 3 copies of and could exercise in the lounge room. But you have to go TO a zumba class as it's so comlex. Oh, shite, where do they come from?