Medical Mystery
After years of unexplained fainting, a 'tilt table test' pinpointed the cause
By Rachel Zimmerman The Washington Post
Published August 3, 2026
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As a child, Janet Mercel was prone to fainting. She remembers passing out in her Upstate New York home, at school and at the grocery store.
But her parents weren't too worried, she said, because she was an otherwise healthy child. The only medical intervention she recalls is a doctor suggesting iron supplements for anemia.
Then, in her 20s, living in New York and working in the fashion and design industry, Mercel began collapsing more frequently: on the subway at Union Square; on a mall escalator into the arms of two teenage boys; in a movie theater. She'd wake up surrounded by concerned onlookers or leaning on someone's shoulder.
Mercel's episodes generally occurred when she was tired, dehydrated, stressed or sick. During a bout of mononucleosis, Mercel drove from a friend's house to her parent's in Red Hook and fainted behind the wheel, hitting a tree. The car was totaled, but Mercel was not hurt.
She grew to recognize the warning signs. Her head and face would get hot, and then she might break into a cold sweat. Her hands and fingers tingled. Her vision would begin to cloud while her ears rang. Sometimes, all the color would drain from her face. If she got out into the air and walked around, she said, she could sometimes stop an episode from escalating. Often, though, there was nothing she could do.
Once, at a now-shuttered restaurant in the East Village, she abandoned dinner with her then-husband and barely made it outside before fainting on the sidewalk. "That time stands out because I remember waking up on a metal grate or bulkhead door and thinking my head was feet from the dumpster and how gross that was," she said.
Despite these episodes, which occurred around three times a week by her late 20s, Mercel, in other ways, appeared to be the picture of health — a super fit exercise enthusiast and avid runner. Her physical abilities, in some ways, made her diagnosis more difficult, she said. "Doctors applauded me on my slow, level heartbeat, years of tests and emergency room visits yielded nothing. I never had shortness of breath, I didn't tire easily. If anything, I had too much energy," she wrote in an essay about her passion for marathon running. "... I could run ten miles, then fifteen, then twenty, but frequently a day later I'd end up in the hospital after my husband found me on the floor, blue lipped and unresponsive."
After one fainting episode on a subway platform, paramedics said that Mercel had a seizure. This led to neurological tests, and, in 2014, doctors theorized she had epilepsy.
That hypothesis turned out to be incorrect. But it would take several more twists — and more fainting — to figure out Mercel's true condition.
Panic attacks? Epilepsy?
One confounding factor was that many of Mercel's symptoms looked as though she was having a panic attack. Sometimes, she said, it was difficult to determine whether panic led to her fainting or whether the physical symptoms before fainting triggered panic. Doctors diagnosed her with an anxiety disorder and over the years prescribed Klonopin, Valium, Lorazepam and several other medications. Early on, a doctor said she was "an overstimulated, high-strung 20-year-old girl," she recalled: "The feedback was, I needed to calm down."
For epilepsy, she was prescribed Levetiracetam, commonly known as Keppra. She remembers being at a work meeting, sitting on a sofa, drooling and barely able to function. She decided to stop that medication: "I said, ‘No, I can't do this. Even if I do have epilepsy, I can't be on this drug.'" After researching the condition, she suspected the diagnosis might be wrong.
In June 2014, Mercel was scheduled for three days of testing at a New York University Langone Health location. Doctors tried to induce an epileptic reaction, she said, but nothing worked. She remembers the hospital as particularly crowded, and she shared a room with a combative patient. This, Mercel said, led to a panic attack and fainting.
The battery of tests included Mercel wearing a Holter monitor, a device that records the heart's rhythm over time. When her heart rate and blood pressure dropped precipitously, Mercel said, a cardiologist was called in for a consultation. But she said routine testing by NYU Langone Health cardiologist Stuart Dickerman showed her pulse and other vital signs to be in the normal range.
Later that summer, Dickerman and other physicians conducted what's known as a "tilt table test," which can help pinpoint the cause of fainting and other symptoms. During the test, Marcel felt dizzy and faint when placed upright at 70 degrees, records show, and then she lost consciousness. While she was being brought back down to a supine position, things got worse. "A pause of 21 seconds was noted in her heart rhythm followed by two beats (measuring 30 bpm) followed by an additional pause of five seconds," records show. "Chest compressions were performed for about 8 seconds. Her heart rate afterwards was 50 bpm. … It was about 2 minutes before the patient was able to open her eyes and verbally respond to her name being called."
Mercel said this is when physicians began saying she had "bradycardia," which simply means a slow heart rate. But in her case, the condition was more severe given her frequent and "dangerously low" heart rate drops and loss of consciousness, said one of her physicians, Larry Chinitz, director of NYU Langone's Heart Rhythm Center and co-director NYU Langone Heart.
The most common reason that people faint is "vasovagal episodes, also known as neurocardiogenic syncope," Chinitz said. "There's a specific reflex, the Bezold-Jarisch reflex, that causes a lowering of heart rate and blood pressure. It's very common." This reflex can cause lightheadedness in some people and fainting in others. Mercel had "a malignant form of neurocardiogenic syncope," Chinitz said, "… a severe version of a common condition that caused repeated loss of consciousness."
Mercel was given the option to enter a clinical trial for what was then a device not yet approved by the Food and Drug Administration: a cashew-size, "leadless" pacemaker.
Unlike a traditional pacemaker, which requires an incision in the chest and wires that run from a battery under the skin into the heart, Chinitz said the leadless pacemaker is a small capsule-like device that's inserted through a vein in the groin and placed directly into the heart. Because the procedure is less invasive, he said, the complication rate is lower compared with that of traditional pacemakers. This device, later approved by the FDA in 2016, produces electrical impulses that prevent the heart rate from dropping below a set point, thereby treating irregular or stalled heart beats.
Also, unlike a traditional dual-chamber pacemaker, which senses and paces both the heart's atrium and ventricle, the device Mercel has "only paces the ventricle," Chinitz said. "It detects when her heart pauses, kicks in immediately and then turns off when her natural rhythm returns. It's very specific in function, but for some patients, that's all they need."
Mercel said her decision was simple: By this time, she had lost weight and felt so sick that she was willing to try pretty much anything. Chinitz implanted the new pacemaker in a procedure that took less than an hour, he said.
However, "it was not a bumpless recovery," Mercel said. She fainted the night of the procedure when a nurse got her out of bed; her sutures popped, and she was bleeding. She also developed deep vein thrombosis at the procedure site a few months later.
Still, she eventually stabilized, fainting far less frequently than before having the pacemaker — but not never. Two years after the device was implanted, Mercel set out for South and Central America to train for a marathon. She contracted Zika in Nicaragua and fainted while training. On the second of two flights home, she fainted on the plane, and she recalls a passenger, possibly a doctor, saying, "She has no pulse."
Upon her return, her cardiologist suggested she not push the marathon running quite so hard — while the pacemaker kicks in to stabilize her heart rate, it doesn't prevent her blood pressure from dropping.
A balancing act
At that point, Mercel was considering having children, but her cardiologist said that the stress of childbirth was too risky. Several years later, she got a second opinion from a female OB/GYN, who believed Mercel's heart could withstand a vaginal delivery. Mercel gave birth to a daughter in 2022.
Mercel has offered testimonials and spoken at two summits hosted by Medtronic, the manufacturer of her pacemaker. She has not been paid by the company, she said, except to cover travel costs.
These days, Mercel, a writer and executive editor of Avenue Magazine, doesn't run as much, instead varying her activities with yoga and biking.
"I was an adrenaline junkie for a long time," the 43-year-old said. "That has subsided. … I'm much better at managing myself before I tip over."
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Rachel Zimmerman is a journalist and writer based in Cambridge, Massachusetts. Her book "Us, After: A Memoir of Love and Suicide" was published in 2024.
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