Jane Charlton was not herself when she woke one day in April 2002, but it was more terrifying than any ordinary morning grogginess – and it did not shift for the best part of three years.

“It was a feeling of being fundamentally wrong in your own body,” Charlton says, attempting to describe what has remained largely indescribable: the symptoms of depersonalisation disorder, the condition that swallowed a huge chunk of her life.

“It was a constant, continuous otherworldly experience,” she says. “It’s a feeling that, if you’re feeling this way, you shouldn’t be existing at the same time. The feeling was of having left myself completely, constantly trying to grasp on to reality, trying to claw back what I’d had a few days ago. Yesterday I had a life, and now I’ve got nothing.”

Depersonalisation disorder, or DPD, is among the most common yet under-recognised psychiatric conditions in the world. According to studies in both Britain and the US, DPD could affect up to 2% of the population – that is, around 1.3 million people in the UK, and 6.4 million in the US.

People with depersonalisation disorder describe a sense of complete detachment, a life lived as an automaton or on autopilot, characterised by an absence of emotions, either good or bad. (You might think of Channel 4’s recent hit Humans, which featured an intelligence trapped, powerless, in the body of a robot.) They feel as though they are observing their life through a plate of glass or a dense fog, or as if it is appearing in a film. Their bodies and their beings have separated; their limbs are no longer their own.

“The best image I could come up with was that I was a little man sat in the back of my head, with the controls, and you can see the inside of your skull and you’re looking out of these two eye sockets,” Charlton says. “When I first spoke to my dad, the words I used were: ‘I’ve gone mad. It’s finally happened, I’ve gone mad.’”

If the studies are accurate, roughly the same number of people have DPD (or the closely associated derealisation disorder) as are diagnosed with schizophrenia or obsessive compulsive disorder. Yet almost everyone with DPD describes years of fearful, isolated frustration without a diagnosis. They endure countless visits to doctors and psychiatrists, who shrug their shoulders in mystification, having never heard of the condition.

Charlton, 32, is intent on ending this bewilderment. She is hoping to bring wider recognition to DPD, offering people a way out of their unique torment and access to the same treatment that eventually rescued her. “It’s slightly different to most other disorders, where people say we don’t have the right treatments or the right doctors to help us. We do. All we need is awareness,” she says.

Gemma Chan in Channel 4’s Humans.

A specialist treatment clinic for DPD opened at the Maudsley hospital in London in 1999 and saw more than 500 patients in its first six years. However, staff at the clinic believe this represents only a fraction of people with the condition, whose diagnosis still often relies more on typing particular search terms into Google than on visits to medical professionals. “Often a turning point in getting better is having a diagnosis,” Charlton says. “If we can do something so simple to bring that diagnosis forward by potentially years, I’m not sure why we haven’t done it yet.”

The earliest writing that attaches the label “depersonalisation” to an overwhelming, clinical sense of separation dates from the late 19th century, since when its symptoms have often been presented as contributory to better-recognised conditions, such as anxiety disorders and depression. However, DPD can also exist in isolation, and the general understanding is that the brain has triggered a natural defence mechanism against extreme anxiety; having reached an arbitrarily defined limit, it has entered a complete emotional shutdown, taking with it sensations of pleasure as well as pain; love as well as hate.

Many people experience some form of temporary depersonalisation in their lives, typically at moments of extreme fatigue or high stress, such as during a car crash, where both the established defence options of fight or flight are removed. A number of recreational drugs also precipitate similar episodes. However, DPD does not always have such obvious prompts, nor does it abate, leaving one stranded in an emotional wasteland.

Charlton was a high-functioning, content, 18-year-old student when her depersonalisation began in the middle of her first year at university. While at a house party with her boyfriend in France, she tried to get high by eating a yoghurt mixed with cannabis, but her symptoms – which might sound familiar to anyone who has smoked a little too much cannabis – were more debilitating and remained far longer than made any biological sense.

An onset of DPD prompted by recreational drug use is not uncommon, and cases are known of regular users suddenly being incapable of snapping out of a high or a comedown. (Charlton had tried cannabis only once before.) But other principal triggers for DPD include a single traumatic event or sustained periods of physical or emotional abuse. Others experience the disorder without ever fully understanding its cause.

Rachel (not her real name), a 23-year-old graduate in fine art, says her depersonalisation descended when she was 18, while she was sitting in her back garden during a break in revision for her A-levels. Although she had had a propensity for anxiety as a child, the onset of DPD was immediately severe and left her in a zombie-like state. “I fully, fully thought that I’m dead, everything is completely futile,” she says. “And if I’m not dead, then I just don’t care enough about anything to be properly applying myself to any of this.”

Rachel is the daughter of a GP, but although he was wholly sympathetic and led the search for help for her condition, he was initially as unaware of DPD as anyone. He eventually found details of DPD on the internet, leading to a watershed moment in his daughter’s struggles. She was then able to begin a process of learning that led her to the Maudsley.

“It’s such a clever way for your mind to deal with anxiety, but it completely fucks you up,” Rachel says. “So many people must suffer from it, but there is literally no information. My dad found that one article on one little website and without it I would have been screwed.”

Journalist Jeffrey Abugel, who has written two books on DPD.

Whatever the trigger for DPD, sufferers report remarkably similar symptoms. They talk of barriers between consciousness and real life, of emptiness, futility and estrangement. Two books by the American journalist Jeffrey Abugel are entitled Feeling Unreal, and Stranger to Myself after the refrains of people experiencing DPD. Charlton independently came up with the image of the little man sitting in her skull, but was then amazed when she found a sketch online depicting precisely the same figure. It remains high on a Google image search for DPD.

DPD is different from psychosis or schizophrenia in that people with the disorder are never convinced of an alternate reality, that objects or people have become something or someone they are not. Instead, DPD presents a world of metaphor and simile: people talk often about their experiences “feeling like” or “as if” something unusual has occurred.

Moreover, people with DPD often do not appear at all unwell or different to even their closest acquaintances; despite experiencing a total lack of empathy, friends and family do not notice any marked change. The person with DPD is often able to sleepwalk through daily life, and even to maintain close relationships, but is robbed of the emotional peaks and troughs of normal human existence. It only enhances sensations of detachment.

This unity of experience among people with DPD has allowed medical specialists not only to conclude without doubt that it is a real and present condition, but also to create a checklist for people reporting symptoms, aiding both diagnosis and treatment.

Although research into what causes DPD is still at a relatively early stage, brain imaging studies and investigations into fluctuations of skin conductance and heart rates offer some hints. Psychologists have detected what appears to be a disconnection between the parts of the brain governing emotion and those determining rational thought. During studies, subjects may say that they feel anxious or frightened by prompts known to cause stressful reactions, but their bodily responses remain unchanged.

“Somehow that lack of congruence between the way they’re feeling mentally and the way they’re feeling physically adds to this feeling of being cut off and alienated from the world,” says Anthony David, professor of cognitive neuropsychiatry at the Maudsley, and the founding director of the DPD clinic.

Psychologists have detected in DPD sufferers what appears to be a disconnection between the parts of the brain governing emotion and those determining rational thought. Photograph: Nick Dolding/Getty Images

Depersonalisation brought on by recreational drugs may also offer clues. “There’s obviously a biochemistry that might be important as well, a change in neurotransmitters in the brain that might lead to this sort of state,” David says.

Various medications used to treat anxiety disorders and epilepsy have helped in some instances of DPD, but none are yet known to be effective in all cases. David outlined contemporary research using transcranial magnetic stimulation, which can adjust the relative influences of the brain’s various sections and may in time turn out to be a therapeutic option for people with DPD.

Presently, the most effective treatment is a slight variation on cognitive behavioural therapy, focusing on breaking the vicious cycles into which patients can become ensnared. People experiencing DPD find themselves dwelling on their peculiar sensations, which can often exacerbate them, and withdrawing from social interactions, which can serve to heighten the extreme sense of separation. As symptoms persist, sufferers grow demoralised and fear there to be no solution, which can further ingrain despair.

“It’s hard work to function, and sometimes people will just give up,” says Dr Elaine Hunter, the lead psychologist at the Maudsley clinic. “[But] we have techniques for dealing with the content of thoughts. We can deal with the processes, try to interrupt the processes. We can deal with the avoidance.”

Many patients seek out conditions where they know their symptoms will be less extreme: often away from bright lights and repeating only a familiar routine; the habits of a recluse. Both Rachel and Charlton told me how boring their long episodes of solitude became. Charlton could muster the energy only to play Yahtzee against herself for hours at a time and latterly, during her recovery, postponed her university studies to work in a bookshop, where she relished the monotony of stamping books and stacking shelves.

Despite completing her degree, Rachel says that her depersonalisation means she still cannot fully engage, and resents the time her illness has already cost her. “I know that I’m intelligent and capable of quite a lot, but I know that I’ve spent so much of the last five years actually doing nothing, just ruminating and thinking about the state of myself. I’ve lost so much time,” she says.

Although most people with DPD tend to be in their late teens or early 20s, many others have endured the disorder for decades, having abandoned attempts to be believed and understood, much less cured. Allen Killick, who is 72, first suffered from DPD in 1954 and still vividly remembers its onset.

Jane Charlton: ‘When I first spoke to my dad, the words I used were: “I’ve gone mad.”’ Photograph: Linda Nylind for the Guardian

“I was playing football at school,” Killick wrote in an email. “For some reason I looked down at my hands and my mind said, ‘They are not yours.’ I just started screaming and running in every direction in absolute horrendous fear.”

When he was only a few months old, Killick’s house was destroyed by a V2 rocket and he was rescued from beneath the rubble after being missing for two days. He subsequently endured a childhood of extreme physical and psychological abuse from both his parents and grandparents, precipitating (according to psychologists now) the disorder that still plays a large part in his life.

Throughout the years, he has been institutionalised more than once and given ineffective medications that have inhibited all other functions. In the mid 1970s, he says he spent two years as a virtual hermit, confined to his bedroom. Killick has also, however, married and had children, and has held down a number of jobs, using advice from psychiatrists, psychologists and self-help books to make the most of periods between extreme DPD episodes.

“I have had times when I have felt better, but even to this day I have never felt totally me,” he says. “I feel one of the hardest things about DPD is trying to pretend you’re normal when you’re dealing with people, when all I want to do is run away ... I try to suffer in silence with this as if I try to explain it to anyone, just nobody apart from fellow sufferers knows what I am talking about.”

Charlton’s campaign to raise awareness is aimed squarely at helping people with DPD overcome the feeling of isolation. She has written to her MP, the Institute of Psychiatrists and the Department of Health, hoping at least to secure a mailshot to every GP in the country outlining the condition. She recently visited the headquarters of Rethink Mental Illness to brief the charity’s team of advisers in recognising the symptoms of DPD.

Staff at the Maudsley say that, with help, the influence of even the most extreme cases of depersonalisation can be reduced. It is not always a quick fix, but they also hope to be able to educate clinicians across the country in at least setting patients on to the right track.

Killick wrote: “I have had for the last 61 years a PERMANENT feeling that I do not exist. Nothing I do or think seems to be able to change that feeling. I just want to be me, whatever that me is. I long for that so much.”

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