It seems that you are going too fast!
Usually, 30kHz is very efficient, 2.5kHz has a stronger feeling and 15Hz is mild, due to its lower frequency. But everyone can react differently.

Excerpt from this page
http://www.emz.maestro-zapper.com/e_how_to_use_it.html


“This material (zappers) is not a toy.”
“The Zapper’s family has the good reputation of removing a lot of parasites, and this, very quickly, not without some annoyance :”
“A part of this mass is either digested, or evacuated, creating sometimes a state of slight dizziness, nausea, foul-smelling flatulence, headache, itching or stiffness at the joints, irritated skin, tiredness and somnolence (as after a large meal) etc. (thanks, God, not all together or at the same time !)”
“After the first zapping session, immediate or delayed tiredness may occur for few minutes or hours.”
“This is probably due to the sudden release of toxins from dead parasites; the gas usually is from killed intestinal worms.”
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“If side effects are TOO disturbing, it is because the session is TOO strong FOR YOU”
“Decrease the exposure and/or postpone for 1 or 2 days the following sessions, until your body takes control again of its cleansing.”
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The remaining information of this page should interest you, specially the “first time use” chapter.

Welcome to zapping.

Some have had severe die off. You should go slow in the beginning.

WARNING: I recently got a call from a lady who used a 2000 Hz 15 volt "Ultimate Zapper" made by a company in Canada. She told me that the result of using the device was neurological damage that has not cleared up. I doubted that the zapper itself could cause damage and asked her about the details. She had used the unit 40 minutes a day from the first day. The result, she says, has been fairly serious problems that have lasted for a couple years. It appears that she had killed something like candida or Lyme spirochetes so fast that toxins had caused damage. These are research devices only. They are not approved for use on humans. If they are used, they should be used with caution, starting out with 1 minute per day and slowly increasing.

http://www.royalrife.com/zapper727.html

I think Zapping is more powerful than most of us realize! I only recently bought one and started using it--within about a week, I began to get VERY ILL. Since then, for the last month, I have had severe diarrhea and off and on projectile vomiting.

I suspect it has stirred up very old parasites within me! I just posted asking about this. So yes, I am pretty convinced that zapping may be connected, because I suddenly became very sick out of nowhere.

In addition to whatever problems the Zapper may be causing you, nausea can be a symptom of low iodine.