During the great sitcom era, life was simpler. Saner too. We escaped into a world we knew was not real to laugh at characters, some of them quite mad, we clearly knew were made up, like many on "Seinfeld."

Oh, for that era again.

In this new era of reality TV, which more closely mimics life, with its endless challenges and rivalries, the line between real and imaginary has blurred.

What's emerged, report two researchers, is a new ailment of the mind, a sort of mass-media-induced paranoia.

Sufferers are under the delusion that they are living their lives as the stars of a reality TV show. They believe the world around them is an elaborate TV set, filled with actors, and they are the central star in what is in essence a giant reality TV show.

The researchers have dubbed this illness the Truman Show Delusion after the 1998 movie in which Jim Carrey plays Truman Burbank, an insurance salesman who suddenly realizes that he has unwittingly lived his entire life on a huge TV set while the rest of the world watches.

That was a somewhat funny movie. There's nothing funny about the Truman Show Delusion.

One sufferer the researchers came upon visited New York from his hometown to see if the Twin Towers of the World Trade Center were still standing. If they were, he reasoned, he would then know for sure that he was in a reality TV and that the whole collapse of the Twin Towers had been staged just for him.

The researchers are a pair of brothers, Ian Gold, an associate professor of philosophy at McGill University in Canada, and Joel Gold, a psychiatrist at Bellevue Hospital in New York.

Ian Gold describes the Truman Show Delusion this way: "You wake up and suddenly you discover, you don’t know how, that all the people around you have been put there to be characters in your life -- that there are cameras everywhere and the whole physical environment is created."

The sufferer does not believe the whole world has become a reality show, just his or her world. "There is this sense that there is a real world out there beyond this reality TV show," he says.

Joel Gold first came across the delusion when he was working in Bellevue’s emergency ward. From 2002 he saw five cases, and more have popped up since reports of the findings were released.

The brothers say the delusions are not an illness in themselves but rather symptoms of mental illness.

What makes the Truman Show Delusion unique is the scale of paranoia it represents. Typically in paranoia, sufferers believe one or perhaps several people are out to get them. In Truman Show Delusion, they think the whole world is in on it.

The question the Golds ponder is just what has prompted this new ailment to arise. While it may take the form of an imagined reality show, they think the catalyst is elsewhere.

"We are really trying to figure out if there is something about the cultural changes we are experiencing in the western world now,” says Ian Gold.

They're tentatively pointing at the great changes wrought by reality shows and the internet, working together. Their effect has been to vastly expand our universe. Says Gold: “The big change the shows and the internet have brought means we are really living in a global village."

Fifteen years ago, we lived in small circles where unless we were celebrities, the people who knew about us were a small number, measured in dozens.

That’s all changed with the internet, especially with social networking, where the circle widens considerably. We create an imaginary world in which we are the celebrity with whom others interact. That can be great fun and enriching for those with healthy self images.

Not so for paranoids. That far vaster world expands the number of people who could hurt them, from several dozen to the universe at large. They suddenly see themselves as all that much more vulnerable.

“Here I am somebody that is disposed to psychosis,” says Gold.

“I am living through a historical period where the world of possibilities suddenly has grown enormously. I could just get on YouTube or MySpace with something interesting and then I could suddenly be like Brad Pitt. But then that makes the world also that much more threatening because more people could hurt me.”