The first time I can remember feeling like I didn’t exist, I was 15. I was sitting on a train and all of a sudden I felt like I’d been dropped into someone else’s body. My memories, experiences, and feelings—the things that make up my intrinsic sense of “me-ness”—projected across my mind like phantasmagoria, but I felt like they belonged to someone else. Like I was experiencing life in the third person.

What doctors call “depersonalization” is somewhat beyond the power of words to convey, but it corresponds loosely to what Timothy Leary might have been talking about when he came up with ‘ego loss’ in the 1960s—minus the psychedelic drugs and the feelings of being gloriously at one with the world. Though it can be triggered by drugs, it often occurs on its own, and it’s a fairly terrifying experience. Earlier this year my doctor prescribed me a cognitive behavioral-therapy manual called Overcoming Depersonalization and Feelings of Unreality. If Leary’s psychedelic rewrite of the Tibetan Book of the Dead teaches you “how to break free from personality into new realms of consciousness,” this book seeks to reverse the effects.

“It’s a disorder that’s not actually that well-studied,” Dr. Nick Medford, a neuropsychiatrist and researcher at the Brighton and Sussex Medical School in the U.K., tells me. It’s characterized by a pervasive and disturbing sense of unreality in both the experience of self (called “depersonalization”) and one’s surroundings (known as “derealization”); accounts of it are surreal, obscure, shrouded in terms like “unreality” and “dream,” but they’re often conveyed with an almost incongruous lucidity. “It’s like I’m too aware of certain larger aspects of reality,” as a patient says in Feeling Unreal by Daphne Simeon and Jeff Abugel. It’s not a psychotic condition; the sufferers are aware that what they’re perceiving is unusual. “We call it an ‘as if’ disorder. People say they feel as if they’re in a movie, as if they’re a robot,” Medford says.

Chances are that you may have experienced it fleetingly. Studies carried out with college students have found that brief episodes are common in young people, with a prevalence ranging from 30 to 70 percent. It can happen when you’re jet-lagged, hungover, or stressed. But for roughly 1 to 2 percent of the population, it becomes persistent, and distressing. Dr. Elaine Hunter, a clinical psychologist working at the Depersonalization Disorder Clinic in London, U.K., says that it’s frequently misdiagnosed. “People often think it is just to do with depression,” she tells me. While depersonalization can be a symptom of anxiety and depression, it can also occur on its own.

Research suggests that areas of the brain that are key to emotional and physical sensations, such as the amygdala and the insula, appear to be less responsive in chronic depersonalization sufferers. You might become less empathetic; your pain threshold might increase. These numbing effects mean that it’s commonly conceived as a defense mechanism; Hunter calls it a “psychological trip switch” which can be triggered in times of stress.

Dr. Elena Bezzubova, a Russian psychoanalyst who treats people with depersonalization in California, calls it a painful absence of feeling. “A mother comes to me and says, ‘My son is in prison, I received a letter from him. I do not care, but it bothers me. Please prescribe me something to cry.’”

It might be the implications of the numbing, as opposed to the actual numbing itself, that cause the most distress. Have you ever played that game when you repeat a word over and over again until it loses all meaning? It’s called semantic satiation. Like words, can a sense of self be broken down into arbitrary, socially-constructed components?

That question may be why the phenomenon has attracted a lot of interest from philosophers. In a sense, the experience presupposes certain notions of how the self is meant to feel. We think of a self as an essential thing—a soul or an ego that everyone has and is aware of—but scientists and philosophers have been telling us for a while now that the self isn’t quite as it seems. Psychologist Dr. Bruce Hood writes in The Self Illusion that there is no center in the brain where the self is generated. “What we experience is a powerful depiction generated by our brains for our benefit,” he writes. Brains make sense of data that would otherwise be overwhelming. “Experiences are fragmented episodes unless they are woven together in a meaningful narrative,” he writes, with the self being the story that “pulls it all together.” In The Ego Trick, Julian Baggini writes that people are, as the 18th century philosopher David Hume wrote in A Treatise of Human Nature, “bundles of different perceptions.” “The unity [of self that] we experience, which allows us legitimately to talk of ‘I,’ is a result of the Ego Trick—the remarkable way in which a complicated bundle of mental events, made possible by the brain, creates a singular self, without there being a singular thing underlying it,” Baggini writes.

For those who don’t always experience uninterrupted selfhood, this becomes more than theory.

Bezzubova tells me about Henri Frédéric Amiel, the 19th century Swiss philosopher and writer whose posthumously-published journal is thought to include the first reference to depersonalization. “All is strange to me; I am, as it were, outside my own body and individuality; I am depersonalized, detached, cut adrift. Is this madness?,” he writes. But he answers his own question with a resounding “No”: “I have been able to look at things with the eyes of a blind man recently operated upon.”

“In such cases, depersonalization is both a burden, a horrible burden—but it’s in some strange way a blessing, to reach some depths, some meaning which somehow comes only in the broken mirror,” Bezzubova says. “It’s a Dostoyevsky style illumination—where clarity cannot be distinguished from pain.”

This painful clarity might sound a bit grim, but the idea that we can perceive some sort of permanent truth beyond the self is hardly new, and it’s not always nihilistic. Countercultural figures like Leary have made many wary of drugged-up escapism masquerading as revelation, but before the romanticism of the 60s, we had the Romanticism of William Blake and John Keats. “Man has closed himself up, till he sees all things thro’ narrow chinks of his cavern,” William Blake wrote; but on occasion “the doors of perception” might be “cleanse.” While many of the Romantics certainly liked their laudanum, according to James Whittaker, professor of Blake studies at Falmouth University, there’s no evidence that Blake took drugs at all.

Alice is a 59-year-old ex-accountant living in Australia who has had depersonalization for more than 18 years (her name has been changed). However, for her, the experience is pleasant. “It’s helped me in my life,” she says. Over the past few years, she has learned to interpret her experiences in a Buddhist context, and she describes depersonalization as a “deconditioning” of sorts: “The significance I place on the world is all in my mind,” she tells me. While Alice doesn’t exactly equate depersonalization with enlightenment, she sees it as a sort of halfway, formless state. “I believe I am on the path to enlightenment,” she says.

The crossover between dark mental states and Buddhist practices is being investigated by Dr. Willoughby Britton, an assistant professor of psychiatry and human behavior at Brown University Medical School. Britton studies the adverse effects of contemplative practices. Mindfulness has become increasingly popular in the West over the past few years, but as Britton told The Atlantic, the practice in its original form isn’t just about relaxation: It’s about the often painstaking process of coming to terms with three specific insights of the Theravadin Buddhist tradition, which are anicca, or impermanence; dukkha, or dissatisfaction; and anatta, or not-self. Shinzen Young, a Buddhist teacher working with the department of psychiatry at Harvard Medical School, refers to depersonalization as “enlightenment’s evil twin.”

“I’ve sometimes wondered what would happen if I, or someone like me, were to attempt to guide a DP/DR [depersonalisation/derealisation] victim into reframing their hell into heaven,” he tells me.

The Diagnostic and Statistical Manual of Mental Disorders (DSM) notes that depersonalization must cause the patient distress and have an impact on her daily functioning for it to be classified as clinically significant. In this sense, it seems inappropriate to call Alice’s experiences pathological. “We have ways of measuring disorders, but you have to ask if it’s meaningful. It’s an open question,” Bezzubova says. “But [depersonalization] certainly has the quality of being ill. It’s certainly a lack of order—especially in acute depersonalization. People cannot manage their daily activities.”

While an overly clinical approach might not represent the scope of people’s experiences, official terms give people stability. It’s an acknowledgement of what they’re going through; it validates suffering. As Simeon writes in Feeling Unreal, “People suffering from depersonalization disorder don’t appear at a doctor’s or psychiatrist’s office to explore mysticism, philosophy, or the deep blue sea. They make the appointment because they are in pain.”

Medford is wary of fruitless philosophizing around unanswerable questions. “It’s like picking a scab,” he says. Obsessive questioning is a common trait in people with depersonalization, often perpetuating anxiety instead of providing insight. “I think calling it a loss of self is maybe a convenient shorthand for something that’s hard to capture,” he says. “I prefer to talk about experience—because that’s what’s important in psychiatry.”