Hopefully no one will get annoyed if I post a reply to your question, since it doesn't really have much to do with zappers.
I found 2 things that "fixed" my allergies. The first was bio-feedback. There are machines out there, the one I was treated with was called a "Biocom", that can play feedback signals into your system. The "mask" a particular frequency, the frequency of the substance your allergic too to help your body "reset" itself. It definately worked for me. I was treated for mercury, and immediately after the treatment, I had a panic attack and other symptoms for the next several days. But now I can hold a vial of mercury without any reaction or weakness.
There are naturopathic doctors out there that use them in the US. I got treated in London. They are harder to find in the US, because of the FDA and the negative view in general of alternative medicine from the government. The FDA especially doesn't seem to like anything to do with bio feedback machines. Even though many come from Germany, like the one I metioned, and they have been used for years safely.
That being said, the other thing that works well is NAET. I've cleared dozens of allergies using it. Many other people have had good results too. For some people it doesn't work. I've been treated by 2 doctors with NAET. One was a Chiropractor and the other was a Acupuncturist. In both cases it worked, but I think the acupuncture works a little better. Chiropractors usually use acupressure to do NAET, while acupuncturists use acupuncture.
NAET doesn't involve any machines. You just hold the substance your allergic to in a vial, you get the treatment, and then you go home with the strict instructions to avoid anything containing the substance for 25 hours. Its worked for me. I'm much better than before. I still have a way to go, but overall NAET has helped me more than anything, short of getting all the dental work in my mouth fixed.