Dancing Plague

Death and sickness undoubtedly go hand in hand with life in the kingdom of Avalonia. No one will raise an eyebrow (but will shed a tear and raise their cup of ale) if someone succumbs to some weird boils, fever or an arrow to the knee. That's just the same old routine, something to be expected to happen either to you or to someone you know.
Plagues are also nothing new under the sun. They sweep through villages, towns and countries with enormous speed and are extremely hard to shake off. What sets the Dancing Plague apart from the others and has caused such a ruckus is that this epidemic was tied to *having fun* instead of getting a bunch of weird symptoms your body was struggling to fight off and subsequently falling apart.
Dancing Plague is one of the most fascinating episodes of the old empire. At first it was suspected to be a curse or a trickery done by one of the faery wild folk, but no one was actually able to trace any magical influence over the victims.
As the name suggest it is an extremely contagious disease and its main effect is to cause involuntary movements of the whole body that resemble dancing and make the sick individual move and move and move until they fall over from extreme exhaustion. It was sparked by a couple of individuals on the street and quickly spread through the entire town. Anyone who has gotten close to the dancing crowd was unable to resist its calling and joined in the madness whether they wanted to or not. The empire dispatched a legion to try to mitigate this outbreak and for a short while you could have seen a lot of very dashing dancers in full uniform until the entire crowd was shot down from a distance by using trebuchets. The pile of big circular stones serves to this day as a little burial mount to comemorate the victims. And also as a landmark that this place is to be avoided.
The Dancing Plague has never repeated again in history and remains an unexplained affair, although there are many theories and gossips surrounding this event. It had a great impact on society as music and public dance festivities have been abolished for several months, at some nearby places even years.