A teenager girl in England with an unusual brain disorder that causes her to collapse when she laughs has cut off her funny friends.
Billie Hodgson, 17, suffers from cataplexy, which triggers sudden muscle paralysis and can strike whenever she giggles.
Her unusual ailment is a complication of narcolepsy, which affects around 22,500 Britons. As well as laughter, it can also be triggered by excitement, anger or even surprise.
Billie, from Sheffield, has cut down on the amount of time she spends with friends because she feels guilty they won't be themselves around her.
She said: 'I'm a bubbly person so to go from that to feeling like I can't laugh is really strange. I feel like I can't be me. 'My friends try not to be funny and if they make me laugh they feel like they have to apologise.
'When I'm with them, I tend not to be as involved in funny situations to avoid cataplexy and especially in front of those who are not as familiar with it.
'We joke about it like friends do because it's a funny thing in itself, and I have to make light of it. 'If we're eating and everyone is laughing around the table, everyone tries to stop but then the silence makes you laugh.'
She added: 'It's so hard to explain how it feels when I collapse, it's like you have no control over your body - I don't have any control over what's happening.
'I can't speak or respond to anything - but the most frustrating thing is that I'm conscious. I shake, and I can't hold things. 'General excitement triggers it, and since I was diagnosed the triggers have become more sensitive.'
Cataplexy strikes people who suffer from the sleep disorder narcolepsy, which affects the brain's ability to regulate the normal sleep-wake cycle.
It means patients often spend a lot of time awake in bed and suffer bouts of extreme sleepiness during the day. Billie is so tired she has to go to sleep at 7pm to try get a good night's sleep.
But she is often tossing and turning throughout the night, waking up for spurts that last 30 minutes to two hours. She also has to nap in the afternoon to catch up on missed sleep.
The exact cause of cataplexy is debated, but the prevailing theory is that a lack of the hormone hypocretin is to blame. Hypocretin plays a vital role in promoting wakefulness during the day.
When the brain is deprived of it, it seems as though its communication to the rest of the body can snap off at even the slightest trigger.
Cataplexy attacks range in severity, with mild episodes resulting in drooping of facial muscles or eyelids, slurred speech and double vision. More severe attacks may involve a total collapse of the body.
They generally last less than two minutes, and they may only last a few seconds, though some people have repeated attacks of cataplexy which persist for up to 30 minutes.
During both mild and severe attacks, the person stays fully conscious but often feel 'locked' inside their body. Billie, who lives at home with mother Sharon, 49 and sister, Harley, 14, was only diagnosed with cataplexy in March last year.
It came as a surprise to the youngster , who was symptom-free throughout her school years and often enjoyed a chuckle.
She says her first memory of cataplexy is collapsing in the dinner hall at secondary school when she was around 14.
Recalling her first attack, Billie said: 'I remember once walking through school with a friend and we were laughing, then I just fell to my knees.
'Everyone thought I'd tripped but I knew something wasn't right. At first we didn't think it was that serious and the doctor told me everyone shakes when they laugh. 'But when I was diagnosed, I felt mixed emotions.
I was relieved that I finally knew what it was and could then start treatment, but at the same time scared because I didn't know how much it would affect my life.
'It's also a lifelong illness which meant it was quite a big thing to accept.'
There is no cure for cataplexy and the condition's only available treatment involves taking daily sleep-inducing medication to try and control the narcolepsy.
As well as forcing her to avoid social situations, Billie's dreams of becoming a midwife have been thwarted by the rare illness. She now wants to speak out to bust myths around the unusual disorder.
Billie said: 'My dream was to be a midwife but I can't do that because I lose control in my hands. 'It's stopping me from doing what I really want to do and now I don't know what to apply for at university.
I'm anxious about going out and I'm not allowed to drive. 'But I want to speak out and raise awareness because it's not something that many people know about.
'I want to show cataplexy isn't like what people stereotypically think - it can have a major impact on someone's life.'