I learned today that if we are taking high doses of MSM, this can deplete molybdenum. I found that there are brands of MSM with it added. I'm a bit surprised there's nothing about that on this forum (I did a search).
Aside from that, I agree that feelings of weakness etc. can be cleansing reactions. As far as the mercury issue, we can take things like selenium, chlorella, and diatomaceous earth to detox it.