There are acute side effects and there are chronic or long term effects. Just because you don't experience any noticable effects after the immediate moment that you are zapping does not mean that the zapping is not having a longer term effect.
At least one study showed that electrical currents above 1 milliamp causes apoptosis, which is premature cell death. While the body is capable of regenerating these cells, there could be longer term effects on the brain which could result in earlier onset dementia, for example. Increased cell turnover is linked with increased risk of cancer. The reason why is that mutations would be passed on to the next cell before the body has had the chance to correct the mutation.
Rather than zapping at higher and higher power, I suggest trying to supplement your zapping with other means, such as pharmalogical ( parasite drugs), herbal parasite treatments, homeopathic treatments (chemical resonance), nutritional (eat better and the immune system is stronger) etc.