For 23 years Rom Houben was trapped in his own body, unable to communicate with his doctors or family. They presumed he was in a vegetative state following a near-fatal car crash in 1983.
But then doctors used a state-of-the-art scanning system on the brain of the martial arts enthusiast, which showed it was functioning almost normally.
"I had dreamed myself away," said Houben, now 46, whose real "state" was discovered three years ago and has just been made public by the doctor who rescued him.
Steven Laureys, a neurologist at the University of Liège in Belgium, has published a scientific paper saying Houben could be one of many falsely diagnosed coma cases around the world.
Houben is being cared for at a facility near Brussels and now communicates via a computer with a special keyboard activated with his right hand, which is capable of minimal movement. He said his body was paralysed when he came round after his accident. Although he could hear every word his doctors spoke, he could not communicate with them.
"I screamed, but there was nothing to hear," he said, via his keyboard.
Houben then suffered years of being effectively trapped in his own body as care personnel and doctors at the hospital in Zolder tried to communicate with him, but eventually gave up hope that he would ever come round.
The moment it was discovered he was not in a vegetative state, said Houben, it was like being born again. "I'll never forget the day that they discovered me, it was my second birth."
Experts say Laureys' findings are likely to reopen the debate over when the decision should be made to terminate the lives of those in comas who appear to be unconscious but might have almost fully-functioning brains.
Belgian doctors used an internationally accepted scale to monitor Houben's state over the years. Known as the Glasgow Coma Scale, it requires assessment of the eyes, verbal and motor responses. But they failed to assess him correctly and missed signs that his brain was still functioning.
Laureys, who is head of the coma science group and neurology department at Liège University hospital, concluded coma patients are diagnosed falsely "on a disturbingly regular basis". In around 40% of cases diagnosed as vegetative, more careful examination shows there is still some level of consciousness. He examined 44 patients believed to be in a vegetative state, and found that 18 of them responded to communication.
"Once someone is labelled as being without consciousness, it is very hard to get rid of that," he told Spiegel magazine, calling for a systematic overhaul of the methods of diagnosis.
Laureys said patients who are not fully unconscious can often be treated and are capable of making considerable progress.
Around a fifth of patients who suffer serious head and brain injuries spend more than three weeks in a coma. Of those, between 15% and 25% are, technically speaking, still alive but remain in a state of unconsciousness, never to wake up.