While most teenagers struggle to get out of bed in a morning, Louisa Ball might take 10 days to fully wake from her slumber, due to a very rare neurological disorder. So what's it like living with Kleine-Levin Syndrome?
Louisa has slept through holidays, friends' birthdays and half of her GCSEs.
In 2008, aged 14, she had been suffering from flu-like symptoms. She was at her school in Sussex when she started nodding off in class and behaving strangely.
"I didn't know what I was doing, what I was saying, everyone thought 'hey this isn't right,'" she recalls.
"I was hallucinating and after that I don't remember anything. All of a sudden it just went blank and I just slept for 10 days. I woke up and I was fine again."
Her parents Rick and Lottie watched their daughter becoming fidgety and with unusual facial expressions as she sank into sleep. The first time was a frightening experience for them, although Louisa herself says she wasn't scared by the episode, more puzzled.
"It was really weird, no one knew what was wrong, we just thought it wasn't going to happen again. And then four weeks later it happened again."
She was finally diagnosed with Kleine-Levin Syndrome (KLS). There is no known cause or cure but Louisa says it was good to know what it was and that it wasn't life threatening.
The average time it takes to diagnose the condition is four years, because there is no test and so it requires a process of elimination of other disorders.
The disease was named after Willi Kleine, a neurologist from Frankfurt, and Max Levin, a psychiatrist from New York, who identified patients with similar symptoms in 1925 and 1936.
Louisa is unusual as KLS usually affects teenage boys, who can also exhibit hypersexuality and inappropriate behaviour.
As well as excessive sleeping, symptoms include behaviour changes, irritability, feeling in a dream-like state and binge eating, symptoms that can be mistaken for normal teenage behaviour. There are no drugs that have conclusively shown to alleviate symptoms.
People with the sleep disorder narcolepsy fall asleep immediately, but people with KLS might sleep more and more over a number of days before falling into sleep mode.
Louisa says she remembers very little when she wakes up from an episode: "It's just blank - no dreams. Now I'll remember a lot more that's gone on. Before I wouldn't remember anything at all. My dad thinks my brain is learning to cope with it more."
So how do you deal with a disorder that takes over your life so much?
It nearly ruined Louisa's career ambitions, because she slept through most of her GCSEs but her college allowed her to enrol and she is studying sport performance and excellence, with dreams of being a dancer.
At first, her school teachers didn't understand, she says. "They'd give work to my brother for me to do and when I went back to school they expected me to have done it but I'd have slept for 10 days."
Some people with KLS have complained they have lost their friends because they suddenly disappear for weeks on end but Louisa has a close knit group of girlfriends. Some even visit her when she's sleeping, just to check she's ok.
When she wakes up, it takes her a few days to fully come round, and her body is quite stiff so her dancing is affected for while.
"I've never really got upset about it but I sometimes do think 'why me', because I've always been a normal healthy person. But all of a sudden it happened and there's no reason why it happened and that sometimes frustrates me.
"But I've got used to it now and learnt to live with it. I'm a special kid."
The change in behaviour before and during a sleep episode is one of the most upsetting things for Louisa's parents, who take it in turns to remain with her. Doctors have told the family it's crucial to wake Louisa once a day to feed her and get her to the bathroom.
But Lottie admits it can take a while to get her to come round. "I've tried before to literally force her to wake up but she just starts swearing and gets so agitated and aggressive."
After watching a video the family made of her while sleeping, Louisa says: "I look scary, it doesn't look like me, it's like I'm on drugs."
Frustrated by the lack of information in the UK, Louisa was taken by her parents to the Hospital Pitié-Salpétrière in Paris, where researchers are looking into whether it is caused by a defective gene.
Many sufferers have abnormalities in their temporal lobe, the area of the brain involved in behaviour and memory. A scan of Louisa's brain function revealed she does have abnormalities in her frontal lobe but there are no signs that this has affected her behaviour or memory.
The good news is the disease can also disappear just as suddenly as it came on. This normally happens after 10 to 15 years.
But Louisa is currently going through a good period. She was out doing Christmas shopping with her best friend this week and has not had an episode in 13 weeks. A few weeks ago she won yet another dance competition.
"It's almost as if I've forgotten about it because I haven't had one in so long."
Louisa's parents, however, are still watching her constantly for signs she could be heading into a sleep state.
"It's weird - now I've left school I haven't actually had an episode, they probably think I was faking it," she jokes.