To think is to be alive. Yet not everyone who thinks agrees with this famous Descarte truism.

Some people with a rare neuropsychiatric disorder, known as Cotard's syndrome, simply cannot fathom their existence.

Oftentimes, those who suffer from Cotard's delusion think they are walking corpses. Others think of themselves as bodiless spirits that will live forever.

No matter the specific variations, patients with Cotard's experience a profoundly distorted reality, in which they deny the existence of their bodies and their everyday needs.

A common consequence is self-starvation.

In one case study, a middle-aged woman with a history of anxiety and psychosis began experiencing nihilistic delusions. She started saying things like, "I am dead." Then, she stopped eating and refused to take medications.

Another case study involves a 49-year-old man who stopped caring for his bodily well-being and began giving away his belongings.

He refused to eat and thought there were evil people out to kill him. A week after being admitted to hospital, the patient told doctors he was already dead and that "his stomach did not work, his liver was decomposed, his brain was paralyzed, and his face lacked blood".

He stayed motionless in his bed, and claimed to hear voices telling him he was the devil.

About a hundred or so similar cases currently exist in the scientific literature.

The first ever recorded case dates back to 1880, when the French neurologist Jules Cotard described a new type of depression marked by "anxious melancholia, ideas of damnation or rejection, insensitivity to pain, delusions of nonexistence concerning one's own body, and delusions of immortality".

The patient he was describing was a 43-year-old woman who claimed to have no brain, nerves, stomach, or even a soul.

She, too, avoided eating because she considered herself eternal.

A few weeks after doctors prescribed her aripiprazole, a medication used to treat schizophrenia, her symptoms showed improvement.

Today, some scientists suspect that Cotard's may not be its own distinct disease but a symptom of underlying issues like bipolar, schizophrenia, depression, or a history of drug use or seizures.

A 2018 review of Cotard's found that three out of four patients who claimed to be dying were under the impression that viruses or bugs were eating them from the inside out.

One 35-year-old patient thought she could feel worms in her brain.

Another patient asked her doctors, "Why do I need to eat when I'm already dead?"

To this day, very little is known about Cotard's syndrome or why its symptoms overlap with other health conditions.

A review of the literature on Cotard's suggests that nearly 90 percent of patients have depressive symptoms while 65 percent have anxiety.

A fraction report auditory or visual hallucinations.

The good news, however, is that these terrifying symptoms can be effectively treated.

Antipsychotics, antidepressants, psychotherapy, and even electroconvulsive therapy are all typical therapies that can have positive results.

In the best-case scenario, patients with Cotard's syndrome can slip out of their distorted reality in as few as two weeks of drug therapy.