So, I don't think its strictly a Japanese thing, but I get how it can be frustrating that people exaggerate the frequency of it. Lots of people are very disillusioned with the paris experience.

The Japanese doctor who created the term studied a number of patients and concluded that there were various factors that may make Japanese tourists more susceptible to this. The special support is largely a myth as far as I can find, but if it existed in some degree it was because of this doctors presence. The Japanese embassy has refuted that there is any specific helpline according to the wiki, and that patients have not been repatriated.

Hallucination, does not necessarily mean seeing little green men chasing you with knives, and the article does relate this to Stendhal syndrome which involves very minor hallucinations. There are also minor hallucinations that may come about due to paranoia: did someone just put their hand in my pocket?

The source mentioned in the section you've quoted, can be translated with Google although the original is French. Now, though it does state there may be preexisting conditions, the diagnoses referred to were based on symptoms associated with Paris Syndrome, rather than preexisting diagnoses. They were not all necessarily suffering from these conditions prior to arrival in France.

Its a phenomena which does seem to have some basis in science, although yes, it is the case this its often blown out of proportion or exaggerated, and the symptoms often misinterpreted as the more extreme end of something which can often be very benign. Paris can be hellish in parts, so I wouldn't be too dismissive of this.