It was a heart-wrenching call to 911 from David Thornton, who found his 14-year-old daughter's lifeless body hanging from her bedroom door. Her legs were outstretched and her head was down.

Dad: "I think my daughter hanged herself!"
911 Operator: "Is she breathing?"
Dad: "I can't tell for sure. Oh, please, you've got to breathe."
Dad: "Come back Elena, come back."
Dad: "I think she's gone."
Dad: "I don't want to bury my daughter."

The teenager had a strap around her neck. But it wasn't suicide.

Dad: "I hope she wasn't playing one of those stupid games."

Elena was playing something called "The Choking Game."

Incredibly, teens are brazenly posting choking game videos on YouTube. It's a dangerous game where one person literally chokes another until they pass out. It's played worldwide under various names.

"Flat Liner, Space Monkey, Space Cowboy...In Ireland it's the American Dream Game. In France it's called the Scarf Game," says New Hampshire Chief Medical Examiner Dr. Thomas Andrew.

"You can go brag to your friends that you did it. The consequences are your friends are going to come to your funeral," says Thornton grimly.

14-year-old Elena Thornton was a vibrant, straight-A high school honor student outside Milwaukee. She also loved playing softball.

Her journal contained entries suggesting she and her friends were playing the dangerous game.

Following his daughter's death, the grieving dad made a chilling discovery: belts and a bungee cord. He says parents should check their kids' rooms for signs like loose doorknobs or bruises on the neck.

The grieving father says his daughter's death is a warning to all parents: "Any parent who thinks that their child is immune to this...watch this show, start thinking harder, because they're not immune."

While you may have never heard of The Choking Game, teenagers have. 73 per cent told the CDC they'd either heard of the game, done it themselves to get a so-called "high," or helped a friend do it.