1)Start slow: theoretically, zeolites work by trapping toxins in their cage-like structures. but they are also supposed to have the highest affinity for mercury so if it picks up lead first and then come into contact with mercury, it will drop the lead in exchange for mercury. it is then eliminated through the bowels or in the urine. So some people cant really handle all this shifting around of toxins etc.
2) Mercury acts as an antibiotic which inhibits the growth of parasites and when you remove the mercury, the parasites have free reign. This can be especially hazardous if you have a recovering immune system.
3) remove the cause and unnecessary stressors. It is going to be very painful to detox while you're still being poisoned by something. Also, as a side note, some people that I have spoken to have found tremedous success from using spring water instead of normal tap water.