I'm not exactly sure how bad my mercury situation was before I began chelating. Not as bad as some of the horror stories I've read about.

My chelating history goes something like this:

A bit longer than 6 months with cilantro and chlorella. I didn't take many breaks during this period. I felt fairly horrible for much of the time but nothing I couldn't handle. After 6 months, I felt much better.

Then I changed to the Cutler Protocol for 2 years. The side effects were less. I took more breaks. For 1 year I could feel the progress. Then sometime in the 2nd year my progress slowed and seemed to stop.

I changed back to cilantro and chlorella for the last 4 months or so. I'm more systematic than I was the first time, and I'm taking breaks this time. I've felt definite improvement in 4 months.

Little by little my reactions have become less and less. My off periods last about a week now. The first day of a break I feel bad, but if I take chlorella, the bad feeling goes away. The next few days before I start another round, I generally feel much better. I still have the occasional reaction during an off period. Some of them with an obvious cause and sometimes I don't really know why I feel bad. The reactions are typically mild and go away after a day or so.
I got these reactions while I was using both methods I've tried.