Everyone around you is an imposter disguised as friends and family. Every day, you struggle with the temptation to bite off your own fingers. You wake up one morning and know with certainty that you’re actually dead.

These experiences may sound as if they were plucked from a horror movie, but for a handful of people, symptoms like these are reality. In recent years, researchers have made critical breakthroughs in diagnosing and treating mental disorders, and more and more of the public have come to understand that conditions like depression, bipolar disorder, and schizophrenia are not imagined and can have biological causes and effects. Unfortunately, many mental illnesses still remain misunderstood, stigmatized, and poorly researched. Among these are extremely rare conditions that sound, to any casual listener, like the stuff of nightmares rather than something to be diagnosed at a doctor’s office.

Here are four of the strangest, most perplexing mental disorders that you may never have heard of before.

To a Capgras patient,an imposter wears the familiar face of a loved one. Pixabay Public Domain

Capgras Syndrome

The hallmark of Capgras syndrome is a delusional belief that someone close to you — a spouse, relative, best friend, even a pet — has been replaced by an identical-looking imposter. The patient may fixate on just one person or several, and might do so chronically or in acute, temporary episodes.

One 1991 case study describes a 74-year-old woman who had just been discharged from a hospital after her first psychiatric admission, and had come to another facility for a second opinion: “At the time of her admission earlier in the year, she had received the diagnosis of atypical psychosis because of her belief that her husband had been replaced by another man,” the researchers wrote. “She refused to sleep with the imposter, locked her bedroom door at night, asked her son for a gun, and finally fought with the police when attempts were made to hospitalize her … She easily recognized other family members and would misidentify her husband only.”

Doctors have used several documented cases of Capgras to explore the possible causes and treatments of the delusion, but haven’t come up with any solid answers. Some researchers blame the condition on a failure of simple recognition processes in the brain, with damage caused by a stroke, drug overdose, or other external factor. Others think the problem lies not in recognizing faces, but in a more subconscious emotional response to familiar people.

The condition can occur at the same time as other mental illnesses, most commonly schizophrenia, and often appears in patients with a neurodegenerative disease.

The fingers are often the target of someone with autophagia. Pixabay Public Domain

Autophagia

As if cannibalism wasn’t a horrid enough idea on its own, autophagia takes things further: People with this disorder eat their own flesh. While not specifically categorized in the Diagnostic and Statistic Manual of Mental Disorders, the condition could be classified as a general impulse control problem. This kind of illness involves the failure to hold back from the urge to carry out an act that is harmful to oneself or others.

One example of autophagy is a 66-year-old man who had been admitted to a facility complaining of insomnia who gradually deteriorated into self-mutilation.

“The patient … had been mutilating his fingers for six years,” the doctors wrote. “This behavior started as serious nail biting and continued as severe finger mutilation (by biting), resulting in loss of the terminal phalanges of all fingers in both hands.”

This particular patient benefited from a combination of antipsychotic and antidepressant treatment, but not all cases of autophagia are the same. Sometimes the behavior appears to be a symptom of something else, such as the genetic condition Lesch-Nyhan syndrome. One study, however, examined the occurrence of finger autophagia in five patients who had suffered traumatic spinal injury. The results were baffling: “All patients were intelligent, willing to discuss their issues, and able to identify conditions of stress and isolation in their lives,” wrote the researchers. But they couldn’t establish a link between the patients’ injury pain and their autophagia, and treatments with drugs, counseling, and behavioral therapy produced only mixed results.

Capgras syndrome can cause a powerful delusion that one is only walking among the living, and not truly one of them. Pixabay Public Domain

Cotard Delusion

Appropriately nicknamed walking corpse syndrome, the Cotard delusion is a rare condition in which a person believes that he is dead. In some variations people hold the delusion that they do not exist, or that they have lost their blood or organs.

“I began to believe I was in perdition, or some kind of hell,” wrote Esme Weijun Wang in an essay about her experience with Cotard’s. “I was trying to figure out what I had done wrong, what had condemned me to this afterlife that looked like my real life before I died but wasn’t real — that was the torment of it.”

French neurologist Jules Cotard treated the first recorded patient. Mademoiselle X, as he nicknamed her, didn’t see the point in eating since she was missing all of her organs and “eternally damned.” She died of starvation.

The possible causes of Cotard’s range widely, from an adverse drug reaction to neural misfirings in the amygdala. There have been several cases successfully treated through pharmacology and electroconvulsive therapy. Others, including Wong’s, seem to have cleared up on their own.

It's incredibly rare, but some people request amputations when the limb in question is perfectly healthy. Pixabay Public Domain

Body Integrity Identity Disorder

The prominent symptom of body integrity intensity disorder, also called amputee identity disorder or BIID, is an oppressive belief that one is meant to be disabled. An otherwise healthy person may desire the amputation of a working limb because it does not feel like it belongs.

In one recent case, a woman named Jewel Shuping intentionally blinded herself.

“I don’t think I’m crazy, I think I have a disorder,” she explained in an interview with Barcroft TV. “BIID means that you have a need to be disabled in some way. In my case, it was a need to go blind.”

Before Shuping pretended to be sightless and learned braille before blinding herself by pouring drain cleaner in her eyes. Experts have described this intense commitment to disabling oneself a “mismatch between the mental body image and the physical body” not unlike that seen in patients with body dysmorphic disorder. Researchers say a “knowledge and respect for the desires of BIID individuals” is the first step for beginning successful treatment. Amputating a healthy limb or otherwise disabling oneself intentionally, however, is controversial. In 2000, a Scottish surgeon amputated the legs of two BIID patients only to be met with ire from the medical community and the public.

As with the other disorders, doctors aren’t sure what causes BIID or why it manifests in different ways for different people. And, like the others, it is just too rare to garner the funding and attention researchers would need to make much progress in finding out.