Landmark chronic fatigue trial could treat two-thirds
A therapy that successfully treats two-thirds of children with chronic fatigue syndrome is being trialled for NHS use.
The disease affects one in 50 children, leading to mental health problems and missing school.
"If anyone has done a cross-country [run] or a marathon - that is how it feels all the time," said Jessica, 14.
The trial, on 734 children, will use intensive online therapy sessions to adjust sleeping habits and activity levels.
It also uses a form of behavioural therapy to help children with the disease adapt the way they live.
Studies suggest one in 100 children misses at least a day of class a week because of the disease.
When Jessica - not her real name - was 10, she missed the equivalent of a whole term in one school year.
She was diagnosed with chronic fatigue syndrome (CFS) - also known as myalgic encephalomyelitis (ME) - at the age of 11.
"I can't do the things my friends can do," she told the BBC News website.
"I've missed a lot of birthdays.
"When they have sleepovers, I have to sacrifice that.
"And I can only do mornings at school, so I miss a lot of lessons."
Prof Esther Crawley, a children's doctor and from the University of Bristol, said: "This illness is devastating. About 50% of teenagers are tired, but these children are different - they stop doing the stuff they want to do.
"The first thing they drop is socialising and fun things, then they drop school, so this is very different to teenagers just being tired."
Jessica's mother said: "It has been hell, it has been depressing.
"I have lost friends, she has lost friends.
"She loves Florence and the Machine and her best friends went [to watch the band play live], it is isolating because her friends were doing what her mind wants to do but her body cannot."
Prof Crawley is leading the FITNET-NHS trial, to see if online consultations work and are cost-effective for the health service.
It is being funded by the research wing of the NHS in England, but when the results are out all the devolved health services would then decide whether they wanted to introduce it.
Trials of the scheme in the Netherlands showed 63% of the patients given therapy had no symptoms after six months, whereas just 8% recovered without it.
The scheme offers behavioural therapy sessions to change the way children think of the disease and aims to reduce the time spent sleeping and sometimes cut activity levels.
The approach regularly receives criticism from some activists who argue it treats chronic fatigue syndrome as a disease of the mind.
Prof Crawley said: "A teenager might say, 'You are just trying to change my sleep', but do you know how much biology you actually change?
"Children who come to my clinic have low cortisol [stress hormone] levels in the morning, that is why they feel so terrible; by changing their sleep, we reverse that.
"The stuff we are doing is not a pill, but it might as well be."