In 1688, a 19-year-old Swiss medical student named Johannes Hofer needed a word for something he kept noticing: soldiers and servants stationed far from home who grew pale, stopped eating, and sometimes wasted away — all from missing home. So for his dissertation at the University of Basel, he built one out of Greek: nostos, meaning "homecoming," and algos, meaning "pain." Nostalgia, literally, is "the pain of returning home" — or really, the pain of not being able to.

Hofer wasn't being poetic. He described nostalgia as a real, physical illness, theorizing it was caused by "vibrations of animal spirits" rattling around the brain, and doctors took it dead seriously for centuries afterward. Swiss mercenaries fighting abroad were considered especially at risk, and army doctors kept recording real diagnosed cases well into the 1800s — including thousands during the American Civil War. The only treatment doctors trusted? Send the patient home.