‘It was like being buried alive,” Samantha Miller says matter-of-factly, fixing me with blue eyes as she munches on falafel. “I was exhausted, with terrible joint pains. It was like having flu all the time with no certainty of recovery. I couldn’t do anything. I was trapped.”

Today, she looks vibrant and younger than her 46 years. She is immaculately dressed in 1950s-inspired floral pinks with a fluffy beret and bright lipstick; her blonde hair is twisted prettily and fixed with a white carnation. We’ve met for lunch in a Turkish restaurant in north London and, as we talk, she seems energetic, fun and very sharp. It’s hard to believe she has spent several years fighting her way back from hell.

In the late 1990s, Miller was living in Hampstead, north London, and teaching art at a “short-staffed, under-funded” secondary school. She found dealing with kids tiring. Children still have “the invincibility of youth”, she says. “They haven’t been crushed by anything yet.” She was also a keen mountain biker and swimmer and led a hectic social life. If something needed doing, she would pick up the slack. And she was always striving to be perfect.

Then she got ill. “I had a glandular, viral thing,” she says. It didn’t occur to her to take time off work. “So I was going in with a raging temperature. That was the point at which something changed.” Although she recovered from the illness, afterwards she felt sleepy all the time. A few years later she underwent a back operation and while she was in the hospital she contracted gastroenteritis. “It was horrific,” she says. “I was being physically assaulted from all sides.”

She recovered from the operation and the gastroenteritis, yet she was left unable even to get out of bed. She was exhausted but not sleeping, in constant pain and over-sensitive to sound and light. She couldn’t get downstairs, so her partner left fruit by the bed when he went to work. She felt overwhelmed and vulnerable – she couldn’t sit up, listen to the radio or answer the door (she remembers reflecting that if instead she had been in a wheelchair, having lost the use of her legs completely, she’d at least have had the energy to get to the door).

Whenever she did try to push herself, her symptoms got worse. So she lay there for months, memorising every crack on the walls in the room and staring at a big picture on the wall – an Oxfordshire landscape that she had painted herself. “I’d think, I can’t believe I made that. How can I ever make anything again?”

Although her partner was supportive, she felt that her friends and family didn’t understand. They said things like “I’m exhausted all the time too” and she knew they thought she was somehow choosing to be ill. A particularly painful moment was when her father said: “This is boring now, I think you should get better.” With no life, and no hope of recovery, Miller called on her partner and her twin sister. She asked them to help her to kill herself.

Medical authorities agree it is a genuine condition, but many sufferers still feel they are dismissed as hypochondriacs. Photograph: Dominic McKenzie/The Observer

Chronic fatigue syndrome is one of the most controversial conditions. Researchers, doctors and patients struggle to agree on its name, its definition or even whether it exists. But the prognosis is bad. An analysis in 2005 of trials that followed patients for up to five years concluded that the recovery rate is 5%.

The condition came to doctors’ attention in the 20th century after a series of mystery epidemics in which large numbers of people were struck by unexplained weakness and fatigue. Two striking outbreaks occurred at the Royal Free Hospital in London in the 1950s and at Lake Tahoe, Nevada, in the 1980s, where the illness was nicknamed “Raggedy Ann syndrome”. Then doctors started to see individual cases cropping up in the wider population.

Chronic fatigue syndrome is also known as myalgic encephalopathy or ME (although not everyone agrees that these are the same condition). There is no proven cause and there are no agreed diagnostic tests, but the condition is defined as six months or more of persistent fatigue that disrupts life and doesn’t get better with rest. It is accompanied by other symptoms including impaired memory or concentration, sore throat, tender lymph nodes, headaches and joint and muscle pain. In severe cases, like Miller’s, patients stay in bed for long periods.

The symptoms are very similar to those of flu, and in many cases chronic fatigue does seem to be triggered by viral infections such as glandular fever (although not flu). The body seems to clear the viral infection, but the fatigue stays. Of adults who get glandular fever, about 12% develop chronic fatigue six months later.

Because there is no clear biological mechanism, the condition has often been claimed to have a psychological cause: psychiatrists in the 1970s put it down to “mass hysteria”, while in the 1980s the press cruelly nicknamed it “yuppie flu”, with the implication that sufferers were spoilt young people too lazy to work.

Medical authorities now agree that it is a genuine, discrete condition, even though its causes are debated, but many sufferers still feel they are dismissed as hypochondriacs who need to pull themselves together.

Tim Noakes, a sports physiologist at the University of Cape Town, South Africa, became interested in chronic fatigue after seeing athletes affected by it and realised that it did not fit this stereotype. “I saw too many professional athletes who wanted to run, they were losing everything, and they still couldn’t run,” he says. “The last thing they wanted to do was to be sick.”

He believes the answer to the condition lies in the brain. His work studying athletes with a colleague, Alan St Clair Gibson, left them both convinced that, although there is a physical limit to what the body can achieve, the brain acts in advance of this limit, making us feel tired before any signs of damage occur. In other words, fatigue isn’t a physical event, but a sensation or emotion, invented by the brain to prevent catastrophic harm. They called the brain system that does this the “central governor”.

“The central governor has got its settings wrong. It’s overestimating how fatigued you are,” says Noakes. Most of the research into the idea of a central governor involves subtle shifts at the very limits of performance, often in elite athletes. But what happens if that entire system crashes? The fatigue that normally protects us from pushing ourselves too far might instead become a prison.

Whatever the trigger – virus, overwork, a genetic predisposition or (most likely) a combination of several factors – Noakes argues that in chronic fatigue the boundaries of physical activity narrow tremendously, to the point where patients are essentially immobilised. If he’s right, it would mean that sufferers like Samantha Miller couldn’t “decide” to be more active any more than Mo Farah could decide to shave 20 seconds off his medal-winning times.

But it does hint that their condition might be influenced by psychological factors. Indeed, one of the most robust scientific findings regarding chronic fatigue is that, when patients are convinced that their condition is biological and untreatable, and fear that engaging in activity will be harmful, they are much less likely to recover. “If they believe it’s incurable, it’s incurable,” says Noakes. Although signals from the body are clearly crucial in determining when we tire, ultimately it’s the brain that’s in control.

This also raises the question of whether cognitive and behavioural therapies could be used to slowly push back the brain’s draconian limits. If interval training works for athletes by teaching the central governor that ever-greater levels of exertion are safe, might it also work for patients with chronic fatigue syndrome?

Samantha Miller made a deal with her partner and her sister. She had been referred to a specialist named Peter White at St Bartholomew’s Hospital in London. Please, just give him six months, they said. If you’re still no better after that, we’ll help you to end your life.

I saw too many professional athletes who wanted to run … the last thing they wanted was to be sick Tim Noakes, sports physiologist

Independently of Noakes, White was developing similar ideas about chronic fatigue. He doesn’t call it a central governor, but he too believes that a combination of triggers – genetic, environmental, psychological – overwhelms the body and throws the nervous system out of balance, causing the brain to reduce massively what it considers a safe level of exertion. To try to reverse the change, he developed with colleagues an approach called graded exercise therapy (GET), which is intended to work like an ultra-gentle form of interval training.

The idea is to set a baseline of activity that the patient can maintain safely, then gradually increase it. Each step has to be small, so as not to risk a relapse. Patients report feeling vastly more fatigued than healthy people for a set level of exercise. But White has shown that, after a course of GET, they feel less tired after the same amount of exercise, even though their physical fitness is unchanged. Just as when athletes do repeated sprints, the exercise regime slowly retrains the patients’ brains that each successive activity level is safe.

White also uses cognitive behavioural therapy (CBT), in which therapists work with patients to challenge negative ideas and beliefs that they have about their illness. This is based on the finding that, as long as patients are terrified that any exertion will cause a crash, the fatigue will maintain its grip. CBT encourages them to try out other ways of coping, and to test whether small amounts of activity are all right. The hope is that this will reduce their fear, helping them to realise that perhaps some exertion is safe after all and that they have the chance to recover.

White suggested that Miller try a combination of GET and CBT. “Will I get better?” Miller asked her therapist. “Of course you will,” she replied, and for the first time Miller believed that it might be true.

Her first exercise goal was simply to turn over in bed once an hour. Every few days, she increased her activity slightly until she was able to sit up for five minutes at a time. Later, when she was out of bed, she might try cooking a meal, but the task would be split into parts. Go downstairs. Chop the onions. Go back upstairs and lie down.

As a creative person, she found the total lack of spontaneity hard to accept. But the perfectionism that she feels contributed to her condition helped her.

She kept an activity diary and as the months progressed she was able to do more. “Walk two minutes around the block,” she recalls. “Then walk three minutes. But walking five minutes might put you in bed for three weeks.” She had to stick to the regime, doing no more and no less than the prescribed activity level, no matter how good she was feeling.

If she pushed herself too hard, she would crash. “It takes incredible discipline,” she says. “One slip-up and you are back to square one.” If she broke the rules and tried to do too much, she would start to feel her body go. “I’d feel hot from the feet up, almost like I was being poisoned. Then I’d be ruined for weeks.”

It took five years of grim determination, but she finally clawed her way out of the fatigue and back into a normal life.

Several small clinical trials suggested that Miller wasn’t alone. The results showed that CBT and GET were helpful treatments. But instead of welcoming the findings, patient groups hated them. “That was received like a lead balloon by almost all the patient charities in the UK and abroad,” says White. These groups were very sceptical that a “psychological” treatment like CBT might help patients with CFS and believed that the activity goals of graded exercise therapy were downright dangerous. CFS is a purely physical condition with no known cure, they argued, so anyone helped by either of White’s therapies clearly didn’t have it.

Instead, patient groups advocated an approach called pacing. This helps patients adapt to life within the physical limits set by the condition and encourages them not to do anything that pushes them close to exhaustion. This would make perfect sense if chronic fatigue were incurable. But, according to White’s theories, it could be counter-productive, by reinforcing negative beliefs and acting to maintain the condition rather than allowing patients to recover.

Chronic fatigue syndrome is one of the most controversial conditions. Researchers, doctors and patients struggle to agree on its name, its definition or even whether it exists. Photograph: Dominic McKenzie/The Observer

Who was right? White and his colleagues decided to do a definitive trial. They worked with the biggest UK patient charity, Action for ME, to design and run the five-year study. It included 641 patients, divided into four groups. A control group just got routine medical care – advice on avoiding extremes of activity, plus drugs for symptoms such as depression, insomnia and pain as needed. The other groups got this standard care plus either CBT, GET or pacing, developed into a therapy (adaptive pacing therapy, or APT).

The researchers published their results in the Lancet medical journal in 2011. They found that APT was ineffective; patients in this group did no better than the controls. But GET and CBT were both moderately helpful, reducing fatigue and disability scores significantly more than in the other two groups. What’s more, 22% of patients recovered after a year in the CBT and GET groups, compared with only 7–8% in the other two groups. While that’s still not a great success record, it showed that White’s approach was the best treatment available and demonstrated that recovery from the condition is possible.

If the previous trials had gone down badly, this one was received with absolute fury. The Lancet was deluged by letters criticising White’s methods. Action for ME rejected the findings. One professor called the trial “unethical and unscientific” in a 43-page complaint to the journal, while patients used Facebook to ask: “When is the Lancet going to retract this fraudulent study?”

Instead, the journal published an editorial in support of White and his colleagues, saying that they “should be praised for their willingness to test competing ideas and interventions in a randomised trial”. But it didn’t change the attitude of the patient groups. After working for years to fund, organise and run a definitive trial, White finally had the data that he believed could help other chronic fatigue patients like Miller. Patients attending his clinics welcomed the findings, but he could not persuade ME patient organisations to listen.

The debate over whether chronic fatigue syndrome is biological or psychological still runs hot. In June 2014, two academics from the Essex CFS/ME service at Southend University Hospital posted an article on the website of the British Medical Journal, speculating that chronic fatigue might be a “meme”. This term was invented by the geneticist Richard Dawkins in his book The Selfish Gene (1976) to describe a psychological idea or behaviour that is transmitted from person to person.

The authors of the article argued that several medical conditions through history might be due to memes, such as “railway brain”, a combination of fatigue and psychiatric symptoms that affected travellers on trains in the mid-19th century and was thought to be due to invisible brain damage caused by the jolty ride. Perhaps, they said, some aspects of chronic fatigue are spread in a meme-like fashion too.

There was an immediate campaign to have the article retracted. The ME Association wrote of its members’ shock, anger and concern at the suggestions. In online comments beneath the article, patients accused the authors of “ignorance, bigotry, and outright cruelty”, while their ideas were denounced as “appalling”, “sick and warped” and “batshit crazy”. A few days later, the Essex CFS/ME service wrote to the ME Association distancing itself from the article and saying that the authors were “very sorry for any distress they may have caused”.

What is psychological is physical and what is physical has a psychological perception to it Peter White, Professor of Psychological Medicine

According to White, the problem comes from a mindset that pervades medicine, in which illnesses are seen as either biological or psychological. “The vast majority of doctors have this dualistic understanding of mind and body,” he says. “Go and see a psychiatrist for the mind and a physician for the body.” It’s a distinction that leaves chronic fatigue patients with only two options: their condition is either biological, currently incurable and impermeable to psychological factors; or they’re hypochondriacs who have invented the whole thing. No wonder they are on the defensive.

In fact, argues White, it’s a false divide. The mind and body inevitably interact and reflect each other: “What is psychological is physical and what is physical has a psychological perception to it,” he says. Scientists are increasingly finding that psychiatric disorders such as schizophrenia or depression reflect structural abnormalities in the brain, while neurological problems such as Parkinson’s cause psychological symptoms as well as physical ones.

White points out that, although CBT is often thought of as a psychological therapy, it has physical effects on the body. Several studies have shown that a course of CBT triggers a measurable increase in brain matter, for example, or that it can influence the levels of stress hormones such as cortisol.

A wider shift in attitudes might help patients to accept that physical and psychological factors are entwined in their illness, he argues, without fear of being stigmatised. Chronic fatigue isn’t either biological or psychological. It’s both.

It is now two years since Samantha Miller recovered. “I do more than a lot of women my age,” she says, dipping a strip of pitta bread into her hummus. “I cycled here. I manage to co-ordinate my accessories!” She has to be careful – a challenging bike ride, or getting too stressed at work, can trigger her symptoms. “You have to step back mentally and physically,” she says.

So now she takes sick days when she’s ill, and says no to things.. She works part-time as an art therapist, doing pottery with prison inmates and psychiatric patients with conditions such as bipolar disorder and schizophrenia. Working with clay provides a safe space to talk, she says. “If the conversation gets difficult, you can go right back to the clay.”

She also works as an artist. In one series of pieces, old mementoes – dolls, pinecones, animal skulls – are neatly arranged in ornate frames. She says she likes the idea of rescuing once-precious personal treasures that have become redundant and giving them a new lifeand meaning. She paints too, haunting mindscapes including a black and blood-red labyrinth of hospital beds and arched windows, entwined with the first lines of Thomas Hardy’s poem, The Darkling Thrush: “I leant upon a coppice gate when frost was spectre-gray. And winter’s dregs made desolate the weakening eye of day.”

That poem ends with the joyous song of a frail thrush; from the dark death of winter, a symbol of “blessed hope”.

This is an edited extract from Cure by Jo Marchant, published by Canongate, £16.99. To order a copy from the Guardian bookshop at the reduced price of £13.59, go to www.bookshop.theguardian.com