Halloween may be over, but we're still in a pretty spooky mood — especially after learning about "walking corpse syndrome." As the Washington Post explains, the illness (a.k.a. Cotard's delusion) actually makes people think they're dead. The syndrome was first described in 1882 by Dr. Jules Cotard and it has remained rare, but more than 100 cases have been documented since the French neurologist's discovery. Although people with Cotard's are able to speak and interact with the world like anyone else, they are 100% convinced that they're dead. As one might imagine, people who have Cotard's also tend to have anxiety, depression, and thoughts of suicide. In some cases, though, patients also feel like they're immortal. Because delusions like this can accompany several other mental illnesses (such as schizophrenia), it can be hard to pin down what's actually happening as a result of Cotard's, and what might be a side effect of something else. At this point, there's no agreement about what causes the illness. And, as the Washington Post article describes, it can be years before someone is actually diagnosed with Cotard's. There's also an interesting, potentially related illness out there: Famously described in a 1997 case study, Capgras syndrome is often thought of as almost a mirror of Cotard's. Here, rather than focusing the delusion inward, people's view of others is distorted. Specifically, people with Capgras believe that their close friends and family have somehow been replaced with identical imposters. Patients recognize who those people are, but feel that something is "off" about them, or that they're lacking the usual emotional connection with people they love. Researchers think this lack of a familiar emotional response is also a major part of Cotard's delusion. So, yes, all of this sounds extremely terrifying and unpleasant. And treating Cotard's is often a difficult task. But the good news is that, with a carefully-implemented combo of therapy and antidepressants or antipsychotic medication, it's possible for some patients to return to the land of the living.