I'm fairly sure it was in a collection of short stories, possibly a 'Year's Finest Sci-Fi' or some such, but I haven't had any luck tracking it down.
The story takes place on an Earth that somehow has drifted into an area of non-causality, and things no longer make sense to most humans. One eats a lichen of some sort that was growing, and is fine. His companion then eats the same thing and dies horribly.
The only beings that are doing well are those who were somehow adapted / synced to this form or reality, and it's alluded to that they may have been crazy before it occurred.
The story ends with Earth coming OUT of the area, as it witnessed by one of the adapted creatures attempting to simply walk across a huge gap (as they apparently normally can), and instead falling into it, and the humans expressing some degree of happiness that it is their time again.
Off the top of my head, it FEELS kind of like a Jack Vance story, but I've yet to be able to track it down. Any ideas?