Cotard's Delusion is a condition in which the sufferer is convinced he is dead. In other words, they are zombies in their minds. Cases in medical literature go back to at least 1788. Mental_floss "dug up" ten such cases.
6. In 2009, Belgian psychiatrists reported the case of an 88-year-old man who came to their hospital with symptoms of depression. The man explained that he was dead, and was concerned and anxious that no one had buried him yet. His delusions subsided with treatment.
7. The same doctors also treated a 46-year-old woman who claimed to have not eaten nor gone to the bathroom in months, nor slept in years. She explained that all her organs had rotted, that she had no blood and that doctors who monitored her heart or took her blood pressure were deceiving her because her heart didn’t beat. After multiple admissions to the hospital and a lapse in taking her medication over the next 10 months, her condition gradually improved.