Game this: dancing plagues

Many hundreds in Strassburg began
To dance and hop, women and men,
In the public market, in alleys and streets,
Day and night; and many of them ate nothing
Until at last the sickness left them.
This affliction was called St Vitus’ dance.

Often a dancing plague begins in the throes of jubilant celebration. Groups of revellers dance, music plays and jesters slake their thirst with warm ale. But the dance takes a hold - the kinetic energy increases and refuses to let up. Soon spectators are joining in, a crowd of gyrating peasants writhe, hop and clap their way around town. They can go on for days with no food, finally collapsing due to exhaustion. The clerics blame it on overheated blood. Some chime in, offering a cure - to dance the plague away. Soon halls are cleared out and makeshift dancefloors created to lure in the revellers. Musicians are paid to keep playing. Don't stop - the demons will remain of you stop.

Of course, the dancing plague continues. Only a blessing from a divine fountain can cure it, showered on the crowd. Those who contract the plague will dance for 1d6+1 days and nights, with a 10% cumulative chance of death for every day danced.