Imagine suffering from a mental illness that causes you to believe your significant other is an imposter set on harming you, or which convinces you that books are for eating, or worse yet, that you have somehow become the walking dead. Scary, right?

While only a small percentage of people are forced to live with the disorders described above, the fact remains that 450 million people worldwide suffer from mental illness. In the United States alone, one in four families is affected. While some mental disorders, such as depression, can occur naturally, others are the result of brain trauma or other injuries. Although it is fair to say that any mental illness can be scary for those suffering, there are a few rare disorders that are especially terrifying. Below, we’ve described what we think you’ll agree are the 5 scariest mental disorders of all time.

1. Alice in Wonderland Syndrome

Alice in Wonderland may be pure fantasy, but one of Alice’s more bizarre experiences shares its characteristics with a scary mental disorder. Known also as Todd Syndrome, Alice in Wonderland Syndrome causes one’s surroundings to appear distorted. Just as Alice grows too tall for the house, those suffering from Alice in Wonderland Syndrome will hear sounds either quieter or louder than they actually are, see objects larger or smaller than reality, and even lose sense of accurate velocity or textures. This terrifying disorder, which has been described as an LSD trip without the euphoria, even perverts one’s own body image. Fortunately, Alice in Wonderland Syndrome is extremely rare, and in most cases affects those in their 20s who have a brain tumor or history of drug use.

2. Alien Hand Syndrome

Though it’s often been used in terrifying plot twists, Alien Hand Syndrome is hardly limited to the fictional world. Those with this scary, but fortunately rare, mental disorder experience a complete loss of control of a hand or limb. The uncontrollable limb often seems to take on a mind and will of its own, and sufferers have reported their “alien” limb attempting to choke either themselves or others, ripping clothing, or scratching to the point of blood. Alien Hand Syndrome most often appears in patients with Alzheimer’s Disease or Creutzfeldt-Jakob Disease, or as a result of brain surgery during which the brain’s two hemispheres have been separated. Unfortunately, no cure exists for Alien Hand Syndrome, and those affected by it are often left to keep their hands constantly occupied or use their other hand to control the alien hand.

3. Apotemnophilia

Known also as Body Integrity Disorder and Amputee Identity Disorder, Apotemnophilia is a neurological disorder characterized by the overwhelming desire to amputate or damage healthy parts of the body. Though not much is known about this strangely terrifying disorder, is is believed to be associated with damage to the right parietal lobe of the brain. Because the vast majority of surgeons will not amputate healthy limbs upon request, some sufferers of Apotemnophilia feel forced to amputate on their own — a dangerous scenario. Of those who have had a limb removed by a doctor, most are reportedly happy with their decision even after the fact.

4. Boanthropy

Those who suffer from the very rare — but very scary — mental disorder Boanthropy believe they are cows, often going as far as to behave as such. Sometimes those with Boanthropy are even found in fields with cows, walking on all fours and chewing grass as if they were a true member of the herd. Those with Boanthropy do not seem to realize what they’re doing when they act like a cow, leading researchers to believe that this odd mental disorder is brought on by dreams or even hypnotism. Interestingly, it is believed that Boanthropy is even referred to in the Bible, as King Nebuchadnezzar is described as being “driven from men and did eat grass as oxen.”

5. Capgras Delusion

Capras Delusion, named after Joseph Capgras, a French psychiatrist who was fascinated by the illusion of doubles, is a debilitating mental disorder in which one believes that the people around them have been replaced by imposters. Furthermore, these imposters are usually thought to be planning to harm the sufferer. In one case, a 74-year old woman with Capgras Delusion began to believe that her husband had been replaced with an identical-looking imposter who was out to hurt her. Capgras Delusion is relatively rare, and is most often seen after trauma to the brain, or in those who have been diagnosed with dementia, schizophrenia, or epilepsy.