The former engineering student and martial arts enthusiast, now 46, told the German newsmagazine Der Spiegel that he meditated to pass the long years trapped in his own body.

Houben’s true condition was discovered three years ago when new tests at the University of Liege found that his brain was still functioning.

Using a specially-adapted computer to type messages, Houben has been able to describe the ordeal he endured for more than two decades.

"I would scream, but no sound would come out," he said, "I will never forget the day they finally discovered what was wrong — it was my second birth."

He could hear what was being said around him throughout, but was unable to respond.

"I became the witness to my own suffering as doctors and nurses tried to speak to me and eventually gave up," he said.

The worst moment came when his mother and sister told him of the death of his father and though he wanted to weep, his body remained motionless.

Cut off from the world, he passed his time in thought.

"I dreamed of a better life all the time. Frustration is too small a word to describe what I went through," he said.

His story emerged following an article in a medical journal by the neurologist Steven Laureys, who told Der Spiegel that the problem was it was very difficult to change a coma diagnosis.

"Every patient should be tested at least 10 times before they are diagnosed as being in a vegetative state," he said.

But Houben’s mother, Fina Houben, never gave up hope.

"I always knew our son was still there," she said.

Houben is still unable to move, but he can read thanks to a device set up over his bed, and he communicates through a keyboard.

"I want to read, to talk to my friends with the computer and to live life mow people know I’m not dead," he said.

AFP/Expatica