Re: zappers/frequency generators can make some parasitic worms go to the head area.

That's one reason a plasma device is good to have also. You can use that on the head. Plasma is probably the best method of delivering any frequency because it will penetrate anything and any part of the body. They aren't cheap and you have to watch if they are stable. I'm be getting one.
With zappers you have portability, so you can use them all day and they are low cost. There is a limit to anything.