What kind of chelation are you doing? If you are using DMSA it could be a result of the DMSA because it binds to your magnesium and zinc as well and hg toxic people already are deficient in these two minerals. I know that if I get low in magnesium that I will get strangled on water or food.

It is recommended to only do DMSA for a few days and then to rebuild your stores of nutrients for a couple of weeks. I personally was afraid of the stuff.