In the late 17th century, a medical student named Johannes Hofer noticed a strange illness affecting Swiss mercenaries serving abroad. Its symptoms, including fatigue, insomnia, irregular heartbeat, indigestion, and fever were so strong, the soldiers often had to be discharged. As Hofer discovered, the cause was not some physical disturbance, but an intense yearning for their mountain homeland. He dubbed the condition nostalgia, from the Greek "nostos" for homecoming and "algos" for pain or longing. At first, nostalgia was considered a particularly Swiss affliction. Some doctors proposed that the constant sound of cowbells in the Alps caused trauma to the ear drums and brain. Commanders even forbade their soldiers from singing traditional Swiss songs for fear that they'd lead to desertion or suicide. But as migration increased worldwide, nostalgia was observed in various groups. It turned out that anyone separated from their native place for a long time was vulnerable to nostalgia. And by the early 20th century, professionals no longer viewed it as a neurological disease, but as a mental condition similar to depression.