The first time I used my zapper, the same model as you have, I did exactly the same as you and practically frazzeled myself! I felt very ill for about 24 hours. I actually do not think you can elctrocute or damage yourself with the 9 volts, but I suspect your system/ parasites were not used to it and it just had a reaaly dire effect. I re-started zapping a few weeks later but started doing just 2-3 mins in one go.But of course repeating that 3 times with a sufficiniet gap in between .
The problem with me was I was experiencing toxic dye off off some parasites. I always have to take it easy because my system can only dispose of so much toxicity at a time. I have to take a lot of liver support and Lymph support when i am killing.
Your lymph system could well be stressed if you have been on parasite killing herbs.
Do you know what type of parasites you might have? some are in the blood- filiaria... and lymphatic filiaria camp out in the lymph nodes at night......