In no particular order....prepared to have your mind blown. None of these conditions are found in the Diagnostic and Statistical Manual of Mental Disorders, but would fall into a "Not Otherwise Specified" category of anxiety or adjustment disorders, most likely. I've included links to Wikipedia if you want to read more. (Source: Listverse).
8. Diogenes Syndrome
Diogenes was an ancient Greek philosopher, who lived in a wine barrel and promoted ideas of nihilism and animalism. Famously, when he was asked by Alexander the Great what he wanted most in the world, he replied, “For you to get out of my sunlight!”
Diogenes syndrome, also called Senile Squalor Disorder, is a condition characterised by extreme self neglect, reclusive tendencies, and compulsive hoarding, sometimes of animals. It is found mainly in old people and is associated with senile breakdown.
The syndrome is actually a misnomer since Diogenes lived an ascetic and transient life, and there are no sources to indicate that he neglected is own hygiene.
7. Paris Syndrome
Paris syndrome is a condition exclusive to Japanese tourists and nationals, which causes them to have a mental breakdown while in the famous city. Of the millions of Japanese tourists that visit the city every year, around a dozen suffer this illness and have to be returned to their home country.
The condition is basically a severe form of ‘culture shock.’ Polite Japanese tourists who come to the city are unable to separate their idyllic view of the city, seen in such films as Amelie, with the reality of a modern, bustling metropolis.
Japanese tourists who come into contact with, say, a rude French waiter, will be unable to argue back and be forced to bottle up their own anger which eventually leads to a full mental breakdown.
The Japanese embassy has a 24hr hotline for tourists suffering for severe culture shock, and can provide emergency hospital treatment if necessary.
6. Stendhal Syndrome
Stendhal Syndrome, also called Florence Syndrome, is a psychosomatic illness that causes rapid heartbeat, dizziness, confusion and even hallucinations when an individual is exposed to art, usually when the art is particularly ‘beautiful’ or a large amount of art is in a single place. The term can also be used to describe a similar reaction to a surfeit of choice in other circumstances, e.g. when confronted with immense beauty in the natural world.
It is named after the famous 19th century French author Stendhal who described his experience with the phenomenon during his 1817 visit to Florence, Italy in his book Naples and Florence: A Journey from Milan to Reggio.
5. Jerusalem Syndrome
The Jerusalem syndrome is the name given to a group of mental phenomena involving the presence of either religiously themed obsessive ideas, delusions or other psychosis-like experiences that are triggered by, or lead to, a visit to the city of Jerusalem. It is not endemic to one single religion or denomination, but has affected Jews and Christians of many different backgrounds.
The condition seems to emerge while in Jerusalem and causes psychotic delusions which tend to dissipate after a few weeks. Of all the people who have suffered this spontaneous psychosis, all have had a history of previous mental illness, or where deemed not to have been ‘well’ before coming to the city.
4. Capgras Delusion
The Capgras delusion is a rare disorder in which a person holds a delusional belief that an acquaintance, usually a spouse or other close family member, has been replaced by an identical looking impostor.
It is most common in patients with schizophrenia, although it occur in those with dementia, or after a brain injury.
The paranoia induced by this condition has made it a common tool in science fiction books and films, such as Invasion of the Body Snatchers, Total Recall and The Stepford Wives.
3. Fregoli Delusion
The exact opposite of the Capgras delusion - the Fregoli delusion, also called the Delusion of Doubles, is a rare disorder in which a person holds a delusional belief that different people are in fact a single person who changes appearance or is in disguise.
The condition is named after the Italian actor Leopoldo Fregoli, who was known for his ability to make quick changes of appearance during his stage act.
It was first reported 1927 by two psychiatrists who discussed the case study of a 27 year old woman who believed that she was being persecuted by two actors whom she often went to see at the theatre. She believed that these people “pursued her closely, taking the form of people she knows or meets.”
2. Cotard Delusion
The Cotard delusion, also called the Walking Corpse Syndrome, is a rare psychiatric disorder in which a person holds a delusional belief that he or she is dead, does not exist, is putrefying or has lost their blood or internal organs. Rarely, it can include delusions of immortality.
It is named after Jules Cotard, a French neurologist who first described the condition, which he called “le délire de négation” (”negation delirium”), in a lecture in Paris in 1880.
1. Reduplicative Paramnesia
Reduplicative paramnesia is the delusional belief that a place or location has been duplicated, existing in two or more places simultaneously, or that it has been ‘relocated’ to another site. For example, a person may believe that they are in fact not in the hospital to which they were admitted, but an identical-looking hospital in a different part of the country, despite this being obviously false.
The term ‘reduplicative paramnesia’ was first used in 1903 by the Czechoslovakian neurologist Arnold Pick to describe a condition in a patient with suspected Alzheimer’s disease who insisted that she had been moved from Pick’s city clinic, to one she claimed looked identical but was in a familiar suburb. To explain the discrepancy she further claimed that Pick and the medical staff worked at both locations
Do you think any of these might end up in your manuscripts?