Nostalgia

Apparently Swiss mercenaries in the 17th and 18th centuries used to miss their homeland so much they often succumbed to a form of homesickness, or nostalgia, which could lead to desertion, disability and even death. To help prevent this happening, they were forbidden from singing songs from home known as Kuhreihen, which although they were simple melodies played by cow-herding Swiss, were so melancholic as to bring the condition on.

The Wikipedia article on nostalgia has a hilarious sentence:

“Cases resulting in death were known and soldiers were sometimes successfully treated by being discharged and sent home.”

One of the few cases in those days where medicine hit the nail on the head, I suspect.