The first passenger railroad in the United States—the Baltimore and Ohio Railroad—began construction in 1828. Five years later, in 1833, the country saw its first fatal train accident. As train travel proliferated, train wrecks became “a surprisingly frequent form of disaster,” the historian Richard Selcer writes. And “the single worst type of railroad accident … not to mention the most frequent, was the rear-end collision.”

Passengers involved in these train crashes would sometimes come down with a peculiar constellation of symptoms, including back pain, arm pain, headaches, hearing problems, anxiety, insomnia, lowered sex drive, and memory problems. These symptoms would appear even in the absence of any visible injuries. The condition was known colloquially as “railway spine.”

The physician John Eric Erichsen suggested that it might be caused by the “‘jarring back and forth’ of the spine, although he could not explain what exactly happened to the spinal cord as a result.” So writes Robert Ferrari, a professor of medicine at the University of Alberta, in his book The Whiplash Encyclopedia, noting that “railway spine” in fact bears a striking resemblance to whiplash—a condition also linked to rear-end collisions, but of the automotive kind. (The Mayo Clinic says a whiplash injury “most often occurs during a rear-end auto accident, but the injury can also result from a sports accident, physical abuse, or other trauma.”)

The thing is, “whiplash” is not really a medical condition. It’s a term people use to describe neck pain and other symptoms thought to stem from an “acceleration-deceleration mechanism of energy transfer to the neck,” according to the Quebec Task Force on whiplash-associated disorders, which came up with a classification system for whiplash injuries in 1995. The task force also used the term “whiplash” for the force that causes the injury, not for the injury itself.

A whiplash injury according to this classification can range from a muscle sprain to spinal cord contusions to a fractured vertebra. The latter two are rarer, and can easily be detected. But for the majority of cases, when there is pain with no visible cause, “there is no way to prove or disprove most claims of whiplash injury,” Ferrari writes. “Instead, physicians make ‘educated guesses.’”

That people can experience neck, head, and back pain after a car accident, or some other kind of neck “energy transfer” is not in doubt. What is unclear is whether such an energy transfer can cause chronic, long-lasting pain, and if so, how.

The typical diagnosis for someone presenting with neck pain after an auto accident is a sprain. But a sprain should heal within a couple weeks. And according to one estimate, about 25 percent of whiplash injury patients end up suffering chronic pain.

“Why should neck and back sprains fail to recover when sprains in other parts of the body usually heal without trouble?” writes the psychiatrist Andrew Malleson in his book Whiplash and Other Useful Illnesses. “There is nothing special about neck ligaments and muscles that can account for their failure to do so.”

And there is still no established physical reason why a whiplash injury would cause chronic pain. Given that, and given the involvement of insurance companies in car accidents, it would be easy to think a lot of these ongoing whiplash cases are scams fabricated to get a payout. (A “useful” illness indeed.)

“The average whiplash claimant submits a request for a few thousand dollars,” Malleson writes. “Some claims are genuine, most are greatly exaggerated, and some are totally bogus.” (It’s worth noting that Malleson used to serve as an expert witness for insurance companies.)

In the U.K., which has sometimes been called “the whiplash capital of the world,” a working group by the Faculty of Actuaries estimated that fraud accounts for anywhere between 10 and 60 percent of the country’s whiplash cases—a wide enough range that you might as well say, “We don’t know.”

At any rate, it’s certainly an expensive condition. By one estimate, rear-impact whiplash injuries in the United States have a price tag of $2.7 billion a year, including both economic and quality-of-life costs. If physicians followed the Quebec Task Force’s recommendations for treating whiplash—“Mobilize the neck within 72 hours of the accident, exercise, limit inactivity, and avoid dependence on collars and analgesics”—Malleson estimates that “a few million dollars would cover the cost of such treatment for the whole of North America.”

But Ferrari thinks only a “very small percentage [are] malingering. People aren’t smart enough to malinger.” If someone were to exaggerate their symptoms for the sake of an insurance claim and then continue living their normal life, he thinks they’d be caught pretty quickly.

These patients are “clearly suffering,” he says. “There’s no doubt that if you assess people who have chronic neck pain, you will have physical examination findings that are clearly abnormal. The genuineness of the symptoms should not be the controversy. What should be the controversy is the attribution. To what are you attributing those symptoms and why?”

Filing an insurance claim forces someone to pay close attention to their symptoms, so that they can report them to the insurer and their doctor (and maybe a lawyer)—and the more carefully you’re keeping track of your pain, the more likely you are to notice it. The symptoms could come from many sources, but, Ferrari says, if you were in a collision, “you’re attributing them all to one thing. We are very suggestible individuals when it comes to pain, because we have no way of measuring the causes of those pains. And therefore we can attribute them to whatever makes the most sense for us at the time. And a collision makes a lot of sense.”

At least, it does in the U.S. And the U.K., and Canada, and many European countries. But not everywhere. Studies done in Greece, Germany, and Lithuania have found that almost all the whiplash injury patients surveyed in those countries were healed after four to six weeks—about what you’d expect for a sprain.

The difference, Ferrari thinks, is whether the country in question has a “whiplash culture.”

“Whiplash cultures are those cultures in which there is the expectation that if you’ve been in a motor vehicle collision, you’ll probably have some significant problem as a result,” he says. For example, surveys by Ferrari have found that about half of people in Canada expected that chronic symptoms would follow a whiplash injury, an association that wasn’t found in Greece, Germany, or Lithuania. And another study by Ferrari and colleagues found that people who expected to recover after a whiplash injury in fact did recover more quickly. Pain and belief are deeply entangled.

“I feel like you could almost take a healthy person and do the right things to them, and make them into a chronic pain patient,” Ferrari says.

Though railway spine and whiplash are not the exact same thing, there are obvious echoes. Railway spine sufferers, too, were accused of milking it by insurance companies; there were vague but unproven theories about what might be happening in the body after a train crash; and at one point, Erichsen speculated that “terror” might play a role in what patients were experiencing—in other words, that there could be psychological factors involved, too.

“I think railway spine is an example of how we can easily repeat ourselves,” Ferrari says. “We’re a society that wants to attribute pain, fatigue and other symptoms to some disorder or disease. So we just have this natural tendency to try to make connections that don't make a lot of sense, rather than sitting back and saying, ‘Let's try to understand why there are some people in our society with chronic pain.’”