Although the exact numbers are unknown, it is thought only 500 to 1000 of people worldwide are affected.
The disorder strikes adolescents primarily. At the onset of an episode they become progressively drowsy and sleep for most of the day and night (hypersomnolence), waking only to eat or go to the bathroom.
Mrs Craggy said her son started having problems three years ago while attending intermediate school.
"For the first six months nothing would wake him up - we jumped on his bed, slapped him, made noise, put cold water on him, he just slept on," she said. His condition was put down to a virus.
For two years the family battled to get a name for it, fighting assumptions it was a behavioural problem, before finally having it diagnosed at Starship Hospital.
Typically it was an episodic disorder, with the duration of episodes varying from person to person. The most debilitating factor was excessive sleep and what was often referred to as "brain fog".
At his worst John was sleeping 18 to 19 hours a day. When awake, his whole demeanour could change, often appearing spaced out and confused.
"It's bizarre. John might be up, but his brain hasn't started functioning yet - it is like his body has woken but his brain hasn't," Mrs Craggy said.
It is 18 months since John has attended school, because he is either asleep or unable to function cognitively. "He was quite a bright boy and now with his 'foggy brain' his memory has been affected and he just doesn't remember."
It could be another eight years before it passes. Other people had had the disease for 20 years, she said.
The cruel disorder robbed teenagers of their most important years. "It is very lonely for him. He doesn't go out and is uncomfortable around people.
"As a parent it is sad to see him missing out on life - how do we prepare him for his future?
"With teenagers the worry is normally about where they are and what they are doing - I almost wish that was the case and he was out there having fun," she said.
"He doesn't have a life. He is at home with us - it's a big sadness."
Mrs Craggy knew of only three other people in New Zealand who had the disease. It was isolating, not knowing where to turn to get help. If a relevant supportive disease-based organisation existed, it might be national or international in scope and affected families might live far away. Websites such as www.klsfoundation.org or www.rarediseases.org could help offer support to sufferers and their families.
Yesterday was Rare Disease Day. Its main objective was to raise public awareness about rare diseases and their impact on patients' lives.
