I think John C hit it exactly. That "die-off" can cause all sorts of pains and feel-bads.
To avoid most of that discomfort, take digestive enzymes while zapping and follow that up with a dose of the Lugol'sIodine [6 drops in water] NOT IF ALLERGIC TO Iodine -- to kill the eggs which are released from the dead parasites.
Also, the three herbs at least once a week and also L-Ornithine at bedtime and L-Arginine upon arrising. These wash out the ammonias.
I zap continuous sometimes for several hours. Doesn't hurt to zap 24/7, but NOT without the support of the herbs/enzymes/amino acids.