I found this story on an episode of QI (series N, episode “Noodles”).
In the eighteenth and nineteenth centuries, nostalgia was considered a disease, and was only declassified as a disease (I assume they mean universally? Or perhaps just in the UK and/or US?) in 1899.
It was called “Schweizenkrankheit”, or “Swiss illness”, because Swiss soldiers were prone to it. Why were the Swiss particularly vulnerable to nostalgia? I’m sure I don’t know.
In the American Civil War over 5,000 men were diagnosed with nostalgia, and reportedly 74 people died from it. The Unionist Army was forbidden from playing the song “Home Sweet Home” in case it brought on attacks of nostalgia.
There were a few suspected causes of nostalgia and, like many eighteenth- and nineteenth-century diseases-that-aren’t-really-diseases (like hysteria or masturbation), the “causes” of nostalgia are hysterical:
-Coming from farming stock
As someone who actually does come from farming stock, the last one had me in stitches.