People’s awareness of mental illness is growing on an almost daily basis. While this has undoubtedly helped break the stigma surrounding it and encouraged many people to seek out the help they need, there are some forms of mental illness that remain almost completely unknown.

One of the rarest forms that it can take is cotard delusion, otherwise known as “walking corpse syndrome”, which causes a person to believe that they are already dead, and a case of this unusual illness was dramatically recounted by a doctor on Untold Stories of the E.R.

In the video below, a woman with the illness almost dies for real because of its effects:

Despite being almost unheard of, the first reported case of cotard delusion happened in the 1700s.

The cause of this unusual mental illness remains a mystery, however, doctors have linked it to other better-known conditions including depression, bipolar disorder, and schizophrenia.

Those with the syndrome have also been reported to believe that they are partially dead or that they no longer exist at all.

A former sufferer of the illness, Esmé Weijun Wang, recounted her experience of the syndrome a few weeks after fainting on a flight, saying, “I was convinced that I had died on that flight and I was in the afterlife and hadn’t realized it until that moment.”

She was subsequently diagnosed with a form of bipolar-type schizoaffective disorder and “no longer saw herself as a rotting corpse”.

This was also the case for the young woman in the video above, which points to promising recovery rates for those unlikely enough to develop this rare condition, although so little is known about cotard delusion that it’s impossible to make any definitive conclusions.