The condition, also known as Sleeping Beauty syndrome, is so rare there are only around 1,000 sufferers in the world.
Yet Stacey Comerford, 15, of Telford, UK, is not the only British teenager hit by it as Mitchell Baldwin, 14, of Arbourthorne, Sheffield, England, can sleep for 22 hours a day, only waking to eat in a trance-like state.
Mitchell, who has missed exams and slept through holidays, said: It’s frustrating. Life is passing me by.”
Stacey’s mum, Bernie Richards, says her daughter’s attacks can come on at any time. The longest lasted two months.
Bernie, 53, said: “There’s never any warning. I’ve even found her fast asleep on the kitchen floor.
“When she’s in an episode, she might get up to go to the toilet or get a drink but she’s not awake. I call it sleep mode. When she wakes, she thinks it’s the following day. She doesn’t have any memory of it.
“She needs reassurance during an episode. It’s like she reverts back to being five years old. When she talks, she sounds like a child, but she can’t help it.”
There is no known cure for Kleine Levin Syndrome, although some experts believe that some sufferers do grow out of it.