The earliest known description of exploding-head syndrome, or EHS, dates back to 1876, when Philadelphia physician Silas Weir Mitchell published his paper “On Some of the Disorders of Sleep,” in the Virginia Medical Monthly. Mitchell described the case of a patient he called Mr. V, who experienced a “sense of a pistol shot or a blow on the head.” Mr. V complained of “a noise in my head, which is sometimes like the sound of a bell, which has been struck once … or else I hear a loud noise, which is most like that of a guitar string, rudely struck, and which breaks with a twang.” In 1920, Sir Robert Armstrong-Jones, a Welsh psychiatrist, described several psychiatric patients whose symptoms included terrifying nighttime experiences with “snapping of the brain.”

British neurologist John M.S. Pearce of the Hull Royal Infirmary in the U.K. introduced the name in a 1988 article published in the medical journal Lancet. Since then, there have been dozens of medical articles written on this bizarre and little-known phenomenon.

What exactly do people with EHS experience? Pearce’s 1988 article describes a common set of symptoms among his 10 patients: “a sense of explosion in the head, confined to the hours of sleep, which is harmless but very frightening for the sufferer.” Pearce published a second article  the following year reporting the same phenomenon in 44 additional patients. Today, EHS is defined by the same symptoms experienced by the people in Pearce’s case reports: a sudden loud noise or an exploding sensation in the head, either at the wake-sleep transition or upon waking at night, and abrupt arousal or fright after the event. Some people also see flashes of light, feel hot, experience chest pains and palpitations, or feel an electrical sensation rising from the lower torso to the head.

In recent years, several more articles have documented the phenomenon all over the world: There was the 48-year old man from India who heard a  bomb explode as he tried to fall asleep at night; a 62-year old German gentleman who heard a loud bang nearly every evening; a 42-old Japanese woman and 47-year-old Dutch woman, both of whom reported noises that sounded like someone yelling or cars passing, followed by a flash of light; and a 55-year old man from Slovakia who, once a week for 12 years, experienced an intense bang that woke him from his sleep. In most cases the experience was so jarring that the patients were left terrified, sometimes waking up with palpitations or drenched in sweat.

Many of the authors who published the early reports said that the disorder is rare—but judging by the growing number of anecdotal accounts in recent years, EHS may not be as uncommon as originally thought. Brian Sharpless, an assistant professor of psychology at Washington State University, wrote in his 2014 review of the disorder that because data on EHS is so limited, classifying the condition as rare might be premature. He cited a 2008 study in the German journal Somnologie, which estimated that EHS appears in 13.8 percent of psychiatric patients, 10 percent of patients with a sleeping disorder, and 10.8 percent of healthy people who answered a screening questionnaire. Sharpless also suggested that people may not report symptoms of EHS during a doctor’s visit, out of embarrassment about their unusual symptoms.

No specific risk factors have been firmly established, though the usual suspects—stress, emotional distress, and fatigue—have all been implicated, and some believe that women and people over 50 may be at higher risk. Sharpless also mentioned an interesting (if not traditionally scientific) study by Simon Sherwood, a psychologist and parapsychology researcher at University College Northampton in the U.K., who found a link between EHS, belief in the supernatural, and reported paranormal experiences.

Researchers think that the cause of EHS lies in the brainstem reticular formation, an area of the brain that regulates sensory-motor reflexes, eye movements, motor control, and transitions between sleep and wakefulness. The theory is that as we approach sleep, the brainstem acts as a night watchman, switching off those functions. In EHS, this routine is somehow disrupted, resulting in wild brain-cell firings that cause the perception of loud noises and flashing lights, as well as muscle spasms.

As of now, there are no diagnostic tests for EHS. Researchers considered the possibility that it may be a form of seizure, but EEG testing, which is used to detect epileptic activity in the brain, has not shown epilepsy as a cause. The symptoms of EHS can be so distressing, however, that patients become convinced that they have something very serious, and end up getting tested for other conditions such as strokes or tumors. There is also no specific treatment, although a variety of medications, including anti-seizure drugs and calcium-channel blockers, have been used to alleviate the symptoms. A study by Gautam Ganguly, a neurologist at the University of Southern California’s Keck School of Medicine, suggested that the best treatment for EHS may be simple reassurance that the condition is benign rather than an indication of something more serious. He reported the case of a 57-year-old man whose symptoms had not recurred six months after doctors convinced him that his EHS was nothing more than an inconvenience.

Indeed, it seems that some patients have simply learned to live with the condition. Reading the online posts of people who were convinced that they have the telltale signs of EHS, I discovered that a number of them were relieved to discover not only that the cause of their distressing symptoms had a name, but that the syndrome was benign. I posted a question to the doctors on Sermo, a social-networking site for physicians, asking if any of them were aware of EHS. Only six doctors responded that they had heard of it. Two of them told me that they had actually experienced the frightening symptoms.

Of the two, one of them confided that he has had EHS all his life. The startling thunderclaps occur every few months, always as he is about to fall asleep. “[I] always wondered if it was a ‘psychic seizure,” he told me, referring to a type of partial seizure that can trigger fear and anxiety. He used to ask his family if they heard the noises; over time, he says, he decided “not to get worked up” about the fact that no one else could. “I know it’s just all in my head,” he wrote. Now, when the symptoms set in, he simply lets the explosions come.