I'm the converse to your example, below. I was doing Cutler chelation & was literally bedridden by thiol reactions. I began the Simplified Methylation Protocol, & those symptoms vanished. I was very sick, but became well & able to continue chelation.
Cutler was of some benefit to me, & I still do it after 4 years. (Now on 225 mg ALA, + DMSA.) But it wasn't the big solution I thought it might be. Remember that (i) ALA is a potent antioxidant, & can make you feel good whether you have Hg or not; (ii) Cutler recommends a bunch of support supps + adrenal support where needed (hydrocortisone). I was given quite a lift by those things, which I erroneously put down to chelation at the time.
However I have two friends who have been just about brought back from the dead by the Cutler protocol. (One has retired his bipolar diagnosis; the other his chronic fatigue, ulcers & acute sinus problems.)
The first friend was wiped out by chelation, & was saved when he added a version of the Freddd methylation protocol. The other doesn't know anything about methylation.
With Cutler, I think the degree of improvement depends on the degree to which mercury underlies your illnesses.
I don't think there is a 'right order' in which you should address methylation & chelation.
The effect of methyl-folate on my thiol problems was unique to me, so far as I know: I haven't heard of anyone else having that response.
Your friend's DMSA/circulating mercury hypothesis may well be correct for him - DMSA does do that - but it may not be replicated in others. For example I'm on DMSA today, & am still having a good old crash on the Freddd Protocol.
I found two opinions on methylation's relationship to mercury chelation (Cutler plan frequent dose chelation), from the forum on Onibasu.com.
Somewhere in this there might be a little gem of info to help someone?
(they aren't my comments; I haven't done methylation and can't comment on Cutler chelation's effect on M.E.)
One person said that adding chelation (using DMSA on frequent dose protocol per Cutler's book) allowed him to use methylation supplements without getting side effects from the increased methylation. He said the increased methylation might have been increasing loose mercury in the body, and adding DMSA supplements reduced this problem because DMSA reduced the loose mercury that had been stirred up by the methylation supplements:
"The difference between taking DMSA while taking methylation supps and not taking DMSA is like night and day. Without DMSA - foggy, fluey, tired: with DMSA - clear head, energy, more normal."
Another person commented that ideally, people should do things in a certain order: remove amalgam fillings first, then chelate to reduce body burden of mercury, then start supplements to increase methylation.