I'm familiar with hulda clarks zapper ,I experience the same symtoms after using my zapper ,but It does not use alternating current she designed it to use direct current it is much safer than the ac current and what you are experiencing is yeast die-off(this is a good thing) ,but you can control the yeast die-off by shortening how long you use your zapper the normal cycle is 7 min on 20 min off,7 min on 20 min off ,7 min on .the modified cycle would be- 3 min on 20 min off,3 min on 20 min off, 3 min on ,this way you will not kill as much yeast and not feel as bad the next time( hope this helps you out )