Barrie Miskin was newly pregnant when she noticed her appearance was changing. Dark patches bloomed on her skin like watercolor ink. A “thicket” of hairs sprouted on her upper lip and chin.

The outside world was changing, too: In her neighborhood of Astoria, Queens, bright lights enveloped objects in a halo, blurring her vision. Co-workers and even her doctors started to seem like “alien proxies” of themselves, Ms. Miskin, 46, said.

“I felt like I was viewing the world through a pane of dirty glass,” she added. Yet Ms. Miskin knew it was all an illusion, so she sought help.

It took more than a year of consulting with mental health specialists before Ms. Miskin finally found an explanation for her symptoms: She was diagnosed with a dissociative condition called depersonalization/derealization disorder, or D.D.D. Before her pregnancy, Ms. Miskin had stopped taking antidepressants. Her new psychiatrist said the symptoms could have been triggered by months of untreated depression that followed.

While Ms. Miskin felt alone in her mystery illness, she wasn’t. Tens of thousands of posts on social media reference depersonalization or derealization, with some likening the condition to “living in a movie or a dream” or “observing the world through a fog.”

People who experience depersonalization can feel as though they are detached from their mind or body. Derealization, on the other hand, refers to feeling detached from the environment, as though the people and things in the world are unreal.

Those who are living with D.D.D. are “painfully aware” that something is amiss, said Elena Bezzubova, a psychoanalyst who specializes in treating the condition. It’s akin to seeing an apple and feeling that it is so strange it doesn’t seem real, even though you know that it is, she added.

The disorder is thought to occur in about 1 to 2 percent of the population, but it’s possible for anyone to experience fleeting symptoms.

Mental health providers have sometimes dismissed D.D.D. as its own diagnosis not only because of a lack of familiarity with the disorder, but also because its symptoms overlap with conditions like depression, anxiety or panic disorder.

As new research has emerged, it has become more widely acknowledged and discussed. The second edition of “Feeling Unreal,” a primer on D.D.D. originally published in 2006, was released in 2023. And Ms. Miskin published a memoir on the subject titled “Hell Gate Bridge” last June. The same month, the novel “Please Stop Trying to Leave Me” came out, featuring a protagonist with D.D.D. The author, Alana Saab, knows the disorder well: She was diagnosed several years ago.

“It’s kind of what I would imagine a drug trip would be,” she said of her experience with the disorder. “But it’s 2 in the afternoon and I’m completely sober.”

The Cambridge Depersonalization Scale is widely considered the most reliable measure of the disorder. Patients are asked to rate how often and how long 29 different experiences occur. Examples include feeling like “a robot,” losing bodily sensations like hunger or thirst and seeing a world that now looks “flat” or “lifeless,” like a picture.

People with D.D.D. may feel disconnected from themselves and their surroundings for months or even years at a time. Less commonly, they may also experience auditory distortions — like muffled or louder sounds.

D.D.D. is often associated with a history of emotional abuse or neglect. The symptoms can be brought on by anxiety, depression, the resurfacing of early trauma, major life stressors, cannabis and hallucinogens like LSD, said Dr. Daphne Simeon, an expert on the disorder and the co-author of “Feeling Unreal.”

In some people, there can be multiple triggers, particularly if there is an underlying propensity to dissociate.

“You can meet a person whose first episode was triggered by panic and then it happened again when they got depressed and then it happened a third time when they had a terrible divorce,” Dr. Simeon said.

Researchers have hypothesized that depersonalization/derealization might be part of the mind’s defense system.

“Your body and your mind are telling you something,” Dr. Simeon added. “You’re having an intolerable experience, essentially, from which you then have to detach.”

Jeffrey Abugel, Dr. Simeon’s co-author on “Feeling Unreal,” dealt with D.D.D. for more than a decade before finally getting a diagnosis. He knows exactly where it stemmed from: “Pot, plain and simple,” he said. The drug pushed him “over the edge,” he added, creating a “massive panic attack.”

Mr. Abugel, who is a health and wellness coach, eventually found help. He now offers private consultations and virtual support groups for people with the disorder.

Ms. Miskin’s symptoms improved with a combination of psychotherapy and medication. She restarted her antidepressant and also began taking lamotrigine, or Lamictal, a medicine best known for treating seizures and bipolar disorder.

Recovery was a painful process.

“You have to relearn how to be in the world,” she said, even though “you just want to lay in bed and pull the covers over your head and never come out.”