Ah, the infamous "Paris syndrome".
I attended a conference on this 2 years ago (or was it last year?), and what came out of it is that nothing came out of it. Nobody was able to define the syndrome scientifically or explain with any degree of precision why it happened. Worse, instead of broadcasting documentaries, interviewing people who were once affected and people who knew them, what we got was amateur-level short movies of all things. Yeah, fictional work is always a sound basis for discussion of a supposed real-life medical condition.
The Paris syndrome is just the Japanese/France version of the good ol' culture shock. People going abroad having highly unrealistic expectations and being brought down to earth the hard way. Hits them like a brick. Now, you might argue that this is some kind of special case because 1) the Japanese's view of France is ludicrously dream-like (basically, it's all romance, fashion and beautiful monuments), 2) they're not exactly the most "internationally aware" people in the first place. That might be true, and what's also true is that as a consequence there are many Japanese people in Paris, but it doesn't make the phenomenon itself some kind of geographic/identity-exclusive disorder. France is not special, and the Japanese aren't special either.
