Beware the City of Lights!
Paris syndrome is one of several oddball psychiatric illnesses which strike specific travelers in specific places, like Jerusalem syndrome. In the case of Paris syndrome, the problem is almost completely specific to Japanese tourists visiting Paris for the first time.
The symptoms of Paris syndrome include hallucinations, feelings of persecution (specifically of being a victim of prejudice), depersonalization, anxiety, and the dizziness and tachycardia that come along with it. The syndrome was first described by a Japanese psychiatrist working in France in 1986, and was officially recognized with journal publication in 2004. Luckily the numbers are low, only striking about 20 out of the estimated six million Japanese tourists who visit Paris annually.
The roots of Paris syndrome lie partially in the Japanese media. As much as we in America have idealized Paris, Japan's television and magazine industry have kicked that up times ten thousand. In Japan, Paris is seen as a perfect, beautiful city filled with perfect, beautiful people who all - each and every one - look and dress like runway models. The Japanese media presentation of Paris is also notably affluent, giving the impression that everyone in Paris is rich and constantly swaddled in luxury.
Then you get to Paris and find that it is wonderful, yes, but it is also a real city filled with real people. Just like every city, Paris has crime, and, dirty streets, and homeless people. Some of them are rich and some are poor, some are fat and some are thin, some are pretty and others are ugly and on all three counts, most people fall somewhere in the middle. The chasm between the idealized Japanese vision of Paris and the reality of Paris is significant - big enough that some people simply cannot assimilate the truth before them, and experience a sort of temporary psychotic break.
Paris syndrome is basically an amped-up version of culture shock, the disorientation felt by most travelers who suddenly find themselves in an unfamiliar environment. It doesn't help that Japanese tourists have difficulty with the language and vice versa (although many Parisians speak English, few speak Japanese), not to mention the exhaustion of travel and being a tourist. And while Americans may be armored against certain cultural issues thanks to the stereotype of French people being rude, Japanese people may find it a shock when they encounter what could be considered rude behavior on the part of the Parisians.