The condition, also known as Sleeping Beauty syndrome, is so rare there are only around 1,000 sufferers in the world.
Yet Stacey Comerford of Telford, Shrops, is not the only British teenager hit by it as Mitchell Baldwin, 14, of Arbourthorne, Sheffield, can sleep for 22 hours a day, only waking to eat in a trance-like state.
Baldwin, who has missed exams and slept through holidays, finds the whole experience frustrating.
“It’s frustrating. Life is passing me by,” a major newspaper quoted him as saying.
Comerford’s mother Bernie Richards revealed that her daughter’s attacks could come on at any time. The longest lasted two months.
“There’s never any warning. I’ve even found her fast asleep on the kitchen floor,” Richards said.
“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 said.
The 53-year-old, who is a full-time mother-of-six, describes it like ‘living with Jekyll and Hyde’ because the change in her daughter is like a switch flicking.
“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,” she said.
“When she’s in sleep mode she can be quite moody but she can’t help it.She’s like a toddler who wants to do things her own way. She stamps her foot if she doesn’t get what she wants.
“It’s like having two different kids in the house,” she said.
Comerford started experiencing symptoms about a year ago, but it was only in March that she was diagnosed with the rare condition.
When her illness first emerged, doctors blamed it to her being a moody teenager.
The 15-year-old was referred to the Princess Royal Hospital, Telford, where doctors feared she had a brain tumour.
Comerford was given a brain scan and was also checked for conditions like narcolepsy and epilepsy.
When all the results came back clear, doctors were left perplexed until a neurologist at Birmingham Children’s Hospital eventually diagnosed Stacey with Kleine Levin Syndrome.
“Having a diagnosis means Stacey knows it’s not all in her mind. She’s had that much stick off people. They don’t understand,” she said.
“I was even investigated by the local education authority because Stacey’s school thought I was deliberately keeping her out of school. They’ve stopped now we’ve got a diagnosis.
“I always knew there was something wrong. I know my daughter. She’s gone from a fresh faced teenager, full of energy to sleeping all the time,” she said.
Richards also said that due to her daughter’s rare illness they could not plan anything in advance, as they did not know when she would fall asleep and when she would eventually get up.
“We try and laugh and joke about it because it’s the only way to get through it,” she said.
There is no known cure for Kleine Levin Syndrome, although some experts believe that some sufferers do grow out of it.
Since her diagnosis, Comerford has been put on a high does of a stimulant drug called modafinil to help keep her awake.
“It seems to be working. She’s more awake and it’s improving her quality of life. We will have to see how she gets on,” Richards said.
Comerford, who hopes to go back to school on a part-time basis soon, said: “I’ve missed nine exams and my birthday in November.
“It’s easier now people know what it is. It’s easier to explain to them. Before, people didn’t believe me. That was the hardest thing.
“People would pull faces at school if I said I was tired and needed to go home,” she added.