I agree with Anne.
I also think its not that some of us are particularly more sensitive to toxins - its that we each have a different set of toxic burden. In my case I was severely stressed for several years. Physically I looked fine. But then I got glandular fever, which together with my existing stress sent me over the edge.
The only theory of chronic disease which makes sense is the one of cumulative stress/toxic load. The system seems fine all the way up till it breaks. By then its too late - the damage has been done - and reversing it is not a simple matter of flipping back the switch.
Dynamic systems (some of which I've studied) are frequently of that type. Outwardly it looks as though nothing is changing, but inwardly there comes a point when the system flips catastrophically.
Of course the human body is strong, and I don't believe any of us are damaged beyond repair. But it takes a very special kind of repair. We can't just do the reverse of what got us here. Think of it like a car driving over a cliff. You can't just reverse back up the cliff!