Consciousness is the foundation of the human experience. Lose it even temporarily, however, and it becomes clear how delicate the whole structure is.

This has become clear to certain audience members at the current Broadway production of 1984, which is running until October 8. There have been reports of viewers fainting, vomiting, fighting, and experiencing seizures due to the play’s vivid torture scenes (including electrocution) and confrontational attitude toward the audience (including actors shouting at viewers about their complicity).

Codirector Robert Icke is used to this by now. Before transferring to New York, the production ran for several years in London. Particularly in its first year, he told me, the first-aid charity “St. John Ambulance used to park outside the matinees in advance.” While the New York theater warns attendees of the play’s “graphic depictions of violence and torture,” Icke contends that the play isn’t actually all that explicit. He argues that theatergoers are fainting because of what’s implied. “It isn’t so much staging—we show hardly any violence at all in 1984—it’s about leading the audience to create the unthinkable images in their own imaginations. That way, the images are personal and therefore far more distressing than anything we could depict.”

Whether these faints are provoked by what’s on stage or what’s happening in viewers’ minds, it’s an emotional distress that is prompting audience members to pass out. Physically, they’re probably perfectly safe. So what’s causing them to faint?

Broadly speaking, there are three main types of faints: ones stemming from serious heart problems (cardiac syncope), ones where blood pressure dips due to standing up (orthostatic syncope), and ones caused by specific triggers (reflex syncope). While plenty of animals faint—miniature schnauzers are prone to irregular heartbeats, for instance, and squirrel monkeys can have low blood sugar—reflex faints appear to be unique to humans.

Reflex faints are activated by the nervous system, which slows down the heart rate and/or lowers the blood pressure in response to strain, leading to reduced blood flow to the brain. Triggers for this can be surprisingly benign. For some people, laughing, coughing, swallowing, urinating, or blowing a trumpet can lead to syncope. Win-Kuang Shen, a Mayo Clinic cardiologist and coauthor of the recently published clinical guidelines for assessing and treating syncope, explained that the nervous system doesn’t distinguish between physical and emotional distress; they’re both stress inputs, leading to the same response.

The most common reflex faints are known as vasovagal faints. Generally, when people describe ordinary fainting, they’re referring to vasovagal syncope. “One-third of the population has vasovagal faints,” said J. Gert van Dijk, a neurologist at Leiden University in the Netherlands.

The name derives from “vaso” (blood vessels) and the vagus nerve, which extends from the brain to the abdomen, spreading fibers to major organs like the heart and lungs. The vagus nerve is responsible for regulating heart rate, sweating, and other essential functions. Triggers like the ones mentioned above lead to confusion in the mechanism for controlling heart rate and blood pressure. Vasovagal faints are essentially a protective mechanism.

Let’s take an example. You’re watching a scary movie or a play about ghosts. During the tense bits, adrenaline is released into your bloodstream. This leads your heart to beat faster and the blood flow to your muscles to increase. Essentially, the nervous system is bolstering your energy and preparing you to fight, as it doesn’t make the fine distinction that what’s on screen or on stage can’t actually hurt you. The parasympathetic nervous system, of which the vagus nerve forms part, seeks to calm you down by lowering your blood pressure and heart rate. Sometimes, though, it overshoots, and your blood pressure might drop too much or your heart rate might slow too far.

Emotional faints are the most common kind of faints overall. These can be activated by fear, excitement, or anxiety, such as one might experience at an intense play like 1984. As van Dijk commented, “It looks horrible and it grabs you emotionally. And if you have the type of vasovagal faint which is prone to emotional triggers such as seeing blood or pain, that can certainly evoke fainting in susceptible people.”

Shen confirmed that just thinking about something distressing can be enough to cause fainting. The sight of blood is one reported by many people, but clinicians have also reported faints provoked by hearing bad news, encountering needles, or seeing gore.

This gore doesn’t even have to be real to create a swoony feeling. The long list of movies that have been reported to make viewers faint includes not just contemporary horror films like Hostel and Raw, or dramas with intensely gory scenes like 127 Hours’ infamous arm-sawing. In 1928, a nurse at a San Francisco movie theater reported that Bela Lugosi’s Dracula, which would be tame to modern audiences, caused about 14 viewers to faint each evening.

In the theater world, as well, every so often a new production will give rise to faints. While theater directors may not have access to all the cinematic trickery of, say, horror-film crews, they have one very valuable tool: The scenes are happening live, in real time. “Live performances would be more of a trigger” than recorded ones, said David G. Benditt, a University of Minnesota cardiologist. “The differences between live events and filmed events may be the realism aspect ... Live events look more real.”

The current version of 1984 is the most recent example of fainting-related notoriety, but there have been plenty of others. There was a notoriously bloody staging of Titus Andronicus at Shakespeare’s Globe Theater in 2014. The show counted among its victims a theater critic from The Independent, who called the production both “exceptional” and “unwatchable”—unwatchable, presumably, because she was unconscious for part of it.

A commonality in these cases is in the quality of the acting. Many of the firsthand accounts from the fainting viewers call attention to the intensity of a performance, even when the violence is implied, as in Alan Ayckbourn’s Haunting Julia (staged in 2011), rather than overt.

Accounts of swooning at the theater are nothing new, though. The 1782 premiere of Friedrich Schiller’s Die Räuber, a dissection of evil played out between two brothers, took place in Mannheim, Germany. The naturalistic response by one actor, on receiving news of a character’s death, so shocked the audience that “fainting women had to be helped toward the exits.” More than 200 years later, and audiences are still passing out at the sight of actors on stage.

Of course, this sort of thing is good for publicity. Audience members and critics often feel a morbid curiosity about a piece of entertainment so apparently shocking that it causes people to pass out, and savvy directors and PR staff have played up these reputations to increase buzz.

“Most fainting in the theater is true syncope due to emotional distress triggered by the show,” Shen said. However, some incidents may not be genuine faints. Even medical professionals and the fainters themselves can find it hard to tell the difference. Without blood-pressure and heart-rate monitors, Shen noted, it would be very difficult to distinguish between psychogenic pseudosyncope (PPS)—where there’s no actual loss of consciousness—and the real deal.

In PPS, psychological issues are manifested physically, in symptoms that mimic fainting. As van Dijk explained, “These attacks are usually the result of unresolved psychological trauma, which can be fairly severe.” For instance, Benditt noted, “physical/sexual abuse is reported in about one-third” of patients with PPS.

This means not that some audience members are faking it, but that emotional distress can lead to either a true faint, which can be medically explained, or PPS, which can’t. Researchers aren’t entirely sure what’s happening in the body during the latter. But that doesn’t mean nothing is happening in the body. Benditt said of PPS sufferers he’s encountered, “they are often immune to painful stimuli during the event.”

There are other clues about whether a collapse is a true faint or PPS. There would be catastrophic cerebral harm after several minutes without blood going to the brain, so a person who lies prostrate for 20 minutes or so, without any permanent damage, hasn’t genuinely fainted. But there are also some “very minor indications” that a faint isn’t genuine, neurologist van Dijk mentioned. In actual loss of consciousness, “the eyes are almost always open,” while in apparent loss of consciousness, it’s common to report eyes closed or eyelids flickering, swallowing, and odd postures.

However, he stressed the importance of not stigmatizing fainters and pseudo-fainters, regardless of the cause. Both types can be concerning, in addition to being difficult to distinguish. And “most people who are prone to fainting due to standing ... are also prone to fainting due to fear. It doesn’t mean that they’re psychologically less able to handle stress [or] particularly more frightened than someone else.” So if you swoon at the theater, it may not be a true loss of consciousness. And even if it is, it’s not an indication of weakness.

Shen emphasized, “Reflex syncope is almost always benign. And patients who are prone to reflex syncope shouldn’t be too anxious. Once you’re anxious, it may facilitate more of these spells.” People can “take very simple precautionary steps” like drinking plenty of water, avoiding triggers, and staying seated. But overall, being faint of heart in these situations tends to be, well, only faintly concerning.