Third this! Kind of glad to hear it really. But only because on occasion, which I've told various doctors this, they've decided I couldn't possibly have CFS/ME/FMS because they'd never seen anyone with the condition who didn't also have brain-fog. Which has led to endless hours of lying in bed wondering if maybe I do have it but am just not aware of it. So I asked the hub and he said 'No. Groaning, huffing, puffing, weeping, wincing, canceling things, suddenly having to lie down, pacing the floors at 4am, fits of anger against the world yes, but nothing noticeably different in the brain department.' Maybe it's one of the symptoms I have to look forward to. Yippee.
Do you have orthostatic intolerance? If you don't (or if it is relativelty light), you could have built in resilience against brain fog as well.