"A third of patients get better immediately, a third suffer relapses and the rest have psychoses," Yousef Mahmoudia, a psychologist at the Hotel-Dieu hospital, next to Notre Dame cathedral said.
Already this year Japan's embassy in Paris has had to repatriate at least four visitors - including two women who believed their hotel room was being bugged and there was a plot against them.
Previous cases include a man convinced he was the French "Sun King", Louis XIV, and a woman who believed she was being attacked with microwaves, Japanese embassy official Yoshikatsu Aoyagi said.
"Fragile travellers can lose their bearings.
“When the idea they have of the country meets the reality of what they discover it can provoke a crisis," psychologist Herve Benhamou said.
The phenomenon, has been dubbed the "Paris Syndrome" and was first detailed in the psychiatric journal Nervure in 2004.