I’d never heard of this until seeing the term in a comment posted to a newspaper article.
Excerpt: Jerusalem syndrome is a group of mental phenomena involving the presence of either religiously themed obsessive ideas, delusions or other psychosis-like experiences that are triggered by a visit to the city of Jerusalem . . . The best known, although not the most prevalent, manifestation of Jerusalem syndrome is the phenomenon whereby a person who seems previously balanced and devoid of any signs of psychopathology becomes psychotic after arriving in Jerusalem.