A man suffering from a rare condition that caused him to think he was dead has spoken about the experience of being a "zombie".
The man, identified only as Graham, told New Scientist magazine about his fight against Cotard's syndrome, or walking corpse syndrome, which causes people to believe they are dead, do not exist or have lost parts of their body.
Graham said he believed his brain had died after he tried to kill himself with an electrical appliance in the bath.
"I just felt like my brain didn't exist any more. I kept on telling the doctors that the tablets weren't going to do me any good because I didn't have a brain. I'd fried it in the bath," he said.
"I just got annoyed. I didn't know how I could speak or do anything with no brain, but as far as I was concerned, I hadn't got one."
He said he lost his sense of smell and taste and believed he did not need to eat because of his condition. He added that he spent time in the graveyard because this was "the closest I could get to death".
People with Cotard's syndrome sometimes die of starvation because they think they do not need to eat; others have tried to destroy themselves with acid. The mental illness tends to occur in people suffering from depression.
It was first identified in 1980 by French doctor Jules Cotard. He presented a patient named Mademoiselle X who said that several of her body parts did not exist. She believed she had been eternally damned so she could not die naturallyand eventually starved herself to death.
Graham's brother and carers looked after him, ensuring he ate and cared for himself, but he continued to feel dead and lacked interest in life: "I never had anything to say. I didn't even really have any thoughts. Everything was meaningless.
"I had no other option other than to accept the fact that I had no way to actually die. It was a nightmare."
He was treated by neurologists Adam Zeman and Steven Laureys. His brain scan showed that metabolic activity in large parts of the frontal and parietal brain regions were as low as those seen in patients in vegetative states.
Laureys said: "I've been analysing Pet scans for 15 years and I've never seen anyone who was on his feet, who was interacting with people, with such an abnormal scan result.
"Graham's brain function resembles that of someone during anaesthesia or sleep. Seeing this pattern in someone who is awake is unique to my knowledge."
The doctors found some of the areas affected were those vital to consciousness and the ability to think, create a sense of self and recollect the past.
Zeman added: "It seems plausible that the reduced metabolism was giving him this altered experience of the world, and affecting his ability to reason about it."
Graham has almost returned to normal and is able to live independently. "I feel a lot better now and go out and do things around the house. I don't feel that braindead any more. Things just feel a bit bizarre sometimes."