Nostalgia started life as a medical diagnosis, and it was thought it could kill you.

The word was invented in 1688 by Johannes Hofer, a young student writing his medical dissertation at the University of Basel. He needed a learned name for something German speakers already called Heimweh, "home-ache." So he built one from Greek: nostos, "a return home," and algos, "pain." The result, nostalgia, is homesickness dressed up in Greek.

The patients Hofer had in mind were mostly Swiss. Swiss mercenaries served in armies across Europe, and the condition was common enough among them to be called mal du Suisse, the "Swiss illness." Its reported symptoms went well beyond sadness. Doctors listed fainting and high fever, and some cases were believed to end in death. Soldiers were sometimes treated successfully by being discharged and sent home.

One trigger got special attention. Traditional Swiss herding songs were said to bring on the illness so strongly that soldiers deserted or fell sick. Swiss mercenaries were threatened with severe punishment for singing them.

The word reached English in 1726, still with its clinical meaning. By the 1830s it was being applied to sailors, convicts and enslaved people torn from their homes.

Then medicine began to lose interest. By the 1850s nostalgia was being treated as a symptom rather than a disease in its own right. Army doctors still used the diagnosis in the American Civil War. Union records counted 2,588 cases and 13 deaths in the first two years, according to Etymonline. By the 1870s it had almost vanished as a medical category.

The word survived by changing direction. Hofer's patients longed for a place. The modern sense, a wistful longing for a past time, took hold by about 1920. Etymonline suggests French literary use may have helped. The pain of being far from home became the pain of being far from "back then," a home you can never return to.

Both Greek halves are still at work in English. Nostos is the homecoming that ancient Greek epic cared about, the kind Odysseus spends the Odyssey trying to reach. The pain half lives on in medical words: neuralgia, myalgia and analgesic.