Saoirse Ronan in Brooklyn. Photo: Kerry Brown/FOX Searchlight

From the ads, it would appear that the Academy Award–nominated film Brooklyn tells a romantic story about a complicated love triangle. And it does. But if you’ve seen it, or read the book by Colm Tóibín, you know it’s not really a love triangle between Saoirse Ronan’s Eilis Lacey, her Brooklyn love, and her Irish suitor, or at least not entirely so. It’s also between Eilis, Brooklyn, and County Wexford — as in, the woman and the geographical places themselves.

It’s a film about homesickness, in other words, a feeling we tend to take rather lightly today — it’s a childish emotion, the stuff of summer camps and (maybe) freshman college dorm rooms. In Eilis’s 1950s era, people tended to brush it off, too. But in the years before World War II, stretching back to the 17th century, European and American medicine took this particular type of heartache incredibly seriously. For many years, “hypochondria of the heart,” as it was sometimes called, was considered a “curable disease”; left untreated, the illness could be, and often was, fatal, the mainstream medical community at the time argued.

Homesickness, of course, has been a part of the human experience for as long as people have been leaving home, with recorded reports appearing in stories of the Greek soldiers who served in the Trojan War, writes philosopher Tiffany Watt Smith in her forthcoming book, The Book of Human Emotions. But in the 17th century, the medical Establishment became alarmed after a group of Swiss soldiers were rendered incapacitated by their longing for home. Smith writes:

It began with the soldiers being distracted by thoughts of home – often … brought on by hearing cowbells chiming in the distance. Then it would progress to lethargy and sadness, “frequent sighs” and “disturbed sleep.” Strange physical symptoms followed – lesions, heart palpitations, and from there a “stupidity of mind” – a kind of dementia. Some soldiers died of the illness, wasting away from a refusal to eat.

The only known “cure” was to return home, and many tried to, only to be punished by death for deserting. In 1688, Swiss physician Johannes Hofer published a report on this mysterious epidemic, naming the problem nostalgia, a mash-up of the Greek words nostos (which means a homecoming or return) and algos (which means pain), Smith writes.

Nostalgia, of course, has come to mean something different now, and the meaning began to change around the start of the 20th century. But for about 200 years after Hofer wrote that initial paper, the word was a medical term that meant an intense, and potentially dangerous, longing for home, although doctors never quite agreed upon the symptoms, explained Susan Matt, a historian at Weber State University and the author of Homesickness: An American History. “Not all homesickness was necessarily going to kill you, but if you had a really acute case, it would qualify as nostalgia,” she told Science of Us. “There are lots of different sets of overlapping descriptions: a shortness of breath, palpitations of the heart, dysentery, fever, problems with the lungs. Or it was feeling an acute yearning, and then your body would start to close down.” In his paper, Hofer outlines the case of a Swiss student who moved away from home; in her book, Matt lets the reader peek at some of the details:

He described the plight of a man from Berne, Switzerland, who had gone to Basel in order to study. While there he suffered “sadness for a considerable time,” and then became afflicted with “a burning fever.” His symptoms worsened with each passing day, and it appeared that he would soon die. His doctors concluded that to save him he must “be returned to his native land.” Although he was “half dead” by this time, he was placed on a bed and transported sixty miles back to Berne. As soon as the trip was under way, the patient was suddenly able “to draw breath more freely … to show a better tranquility of mind.” As the party came closer and closer to Berne, “all the symptoms abated to such a great extent they really relaxed together, and he was restored to his whole sane self before he entered Berne.

While researching her book, Matt combed through centuries’ worth of case reports and found that nostalgia was listed fairly frequently as a cause of death for soldiers in some major wars, in particular the Civil War. “Doctors during the Civil War were quite sympathetic to those suffering from it,” Matt said. On the Union’s side, for example, company bands were barred from playing “Home Sweet Home” because it worsened the soldiers’ nostalgia. “People took it so seriously that during the Civil War you could at least be furloughed,” Matt continued, “and often completely discharged, because the only cure for homesickness is returning home.” By the war’s end, more than 5,000 soldiers had received a diagnosis of nostalgia, and 74 Union soldiers had died of it.

In contrast, the death records for World War I list just one soldier death as being caused by nostalgia. The short explanation for this is that the Western world had become more mobilized; leaving home was no longer uncommon, and homesickness was at odds with the adventurous spirit many in the early 20th century strove to exude. Today we would likely call what happened to that Swiss student in Hofer’s case report an acute case of anxiety or depression. Even at the height of nostalgia’s classification as a medical condition, physicians never quite agreed on whether it was a discrete disease of an underlying condition that could exacerbate other existing medical problems. In the past few years, there are some small signs that some researchers are again considering homesickness worth taking seriously: A study of Latin American immigrants published in 2011 found homesickness to be a factor in mental illness for this population.

It’s something that Shabnam Etemadi, a psychology PhD student at Tennessee State University, sees often in her work with immigrant and refugee communities. She sees this population struggle with a period of deep loss after arriving to their new home in the U.S., during which they long for their home and the loved ones they left behind. But too many, Etemadi said, don’t have access to mental-health resources that could help them handle those emotions. “They wait until they’re referred to me [by a general practitioner],” she told Science of Us. Many of the immigrants she works carry around deep heartache that eventually turns to headaches and stomachaches, which she sees as psychosomatic symptoms of the mental stress they’re under. “Once they know what anxiety or depression is, then they’re able to say, ‘Oh, well, yeah, I’ve been feeling very sad for the past six months.”

And yet many people who move across the world today can still see their loved ones regularly, thanks to FaceTime and Skype. Shouldn’t advances in communication like this preclude homesickness? It’s not so simple, Matt argues, drawing from her interviews with immigrants and soldiers stationed overseas. True, some do find that it’s easier to be away from home now that it’s easier to stay connected. “But others said that knowing with more accuracy what’s going on at home makes them miss it all the more,” she told Science of Us. “So I think it has this ambiguous effect, in that our modern technology seduces us into thinking connection is easy and painless, and it also seduces us into thinking that return is easy — we’ve got jets, and we’ve got cars, and that obscures the real pain of migration and mobility. It’s sort of brushed under the table, because technology makes everything look so smooth.”

Even going home, as anyone who’s moved away from somewhere knows, doesn’t always fix the problem. In Brooklyn, when Eilis returns to Ireland, her town at first seems just as wonderful and homey as she remembered it, until she realizes that her nostalgia had given her some apparent amnesia about certain irritations of living at home. The narrative mirrors the real-life experiences of thousands. “A lot of migrants end up longing for home when they were in the U.S. and longing for the U.S. when they were back in Ireland or Italy,” Matt said. “A lot of times, people thought they were longing for a lost place, but then they go to that lost place and realize they were longing for a lost time.”

You could say, as Smith does in her book, that homesickness is a word with dual meanings: It’s being sick for home, but also being sick of it. “Never quite belonging to one place or another, in one breath they ache for some distinctive taste or smell of home, and in the next confess that they couldn’t imagine … going back there to live,” Smith writes. “As anyone who’s ever gone home for Christmas knows, occasional bouts of sickening for home must be set against the reminder that going back just might make you very sick of it indeed.”

*Correction: An earlier version of this post stated that Shabnam Etemadi is a psychologist at Tennessee State University. She is a PhD student in psychology at the university.