Rare Mental disorders

Dr. Strangelove syndrome: hands with a life of its own
Alien hand syndrome (or Dr. Strangelove syndrome) is a neurological disorder in which one of the sufferer's hands seems to take on a life of its own.
Sometimes the sufferer will not be aware of what the hand is doing until it is brought to his or her attention. Alien hands can perform complex acts such as undoing buttons or removing clothing.

Foreign accent syndrome: speaking your language with an accent
The syndrome causes people to speak their native language as if they had a foreign accent; for example, an American native speaker might speak with a French-sounding accent. It usually follows a severe brain injury, such as a stroke.

Capgras' syndrome: believing there's an impostor in the family
The Capgras delusion or Capgras' syndrome is a rare disorder in which a person holds a delusional belief that an acquaintance, usually a close family member or spouse, has been replaced by an identical looking imposter.

Triskaidekaphobia: fear of the number 13.
Adolf Hitler was triskaidekaphobic. A specific fear of Friday the 13th is called paraskavedekatriaphobia or friggatriskaidekaphobia. Tetraphobia is the fear of the number 4 in China, Japan, and Korea.

Bigorexia: working out too much
Bigorexia or Muscle dysmorphia is a disorder in which an individual becomes obsessed that they are not muscular enough. Sometimes referred to as bigorexia or reverse anorexia nervosa, it is a very specific case of body dysmorphic disorder (BDD).

Muscle dysmorphia can cause individuals to:
- Constantly check themselves in a mirror
- Become distressed if a gym session is missed
- Take potentially dangerous drugs (e.g. anabolic steroids)
- Neglecting jobs/relationships/family due to exercising