There is a mental disorder known as Walking Corpse Syndrome!
The Cotard Delusion, often called Walking Corpse Syndrome, is a rare mental disorder in which people believe that they are either literally, or figuratively dead. Other beliefs part of the Cotard delusion are that the person thinks they don't exist, are decomposing, or have lost their blood and internal organs. Don't worry, though—it's all in their heads.
The syndrome is named after Jules Cotard, a French neurologist who was the first person to describe the condition. In an 1880 lecture in Paris, Cotard explained that the syndrome can have degrees that range from mild to severe. Self-loathing and despair are seen as mild degrees of the condition. Some of the more extreme ones involve chronic depression and intense delusions!
Luckily, there are numerous accounts of pharmacological treatment. Most commonly, antidepressants, antipsychotics, and mood stabilizers are used to treat people suffering from the Cotard Delusion.