People who suffer from Cotard disorder believe they are dead. They believe that they have died, and are still walking around the mortal world. Many hallucinate their skin rotting, limbs falling off, and refuse to eat because they are dead and dead people don’t need to eat.
It is a very dangerous delusion, as sufferers stop eating, drinking, sleeping, and taking care of their basic hygiene. The scary part is, it is a possible adverse effect of the anti-viral drug acyclovir, the drug typically used to treat herpes.
Sufferers of Capgras syndrome are convinced that their loved ones have been replaced by a doppelganger or imposter. This disorder is a strictly visual disorder, and many patients become upset when they see a family member or close friend, thinking they have been replaced by an alien, or someone who looks exactly like them.
The most interesting part is, that patients only believe this when they see the person. When having a telephone conversation, for example, they believe nothing is wrong.
Ever heard of the book, “The Man Who Mistook His Wife for a Hat”? The author, Oliver Sacks, was a famous British neurologist who suffered from Prosopagnosia, a recognition disorder. People who suffer from this disorder are unable to recognize human faces. They must use other cues to recognise a friend, such as hairstyles, clothing, scent, and voice. If someone changes their hair, or begins using a new shampoo, it can completely throw off someone with Prosopagnosia.
Boanthropy is a condition in which sufferers believe they are a cox or an ox, and start behaving as such. They may spend all their time in a field, eating grass, and walking on all fours.
The validity of this disorder is greatly debated. Many take King Nebuchadnezzar from the bible as an example, who spent 7 years thinking he was a cow. Psychologists have not seen another case quite like the king, and are skeptical as to whether the disorder even exists.
Of course, if someone thinks they are any kind of animal other than a human, psychiatric care is indicated.
Foreign Accent Syndrome
This is a very rare syndrome, having less than 100 cases reported worldwide. The cause is not really known, but the disorder generally proceeds an injury to the brain, migraine, or stroke, but has even developed from a developmental disorder.
This syndrome is named after those who treat it, not those who suffer from it. Sufferers will suddenly start speaking with what appears to be a foreign accent, although still in their native language. Careful analysis shows that the sufferers are articulating vowels differently, but not in any particular accent. To the untrained ear, though, this can sound like specific accents.