Tens, hundreds, sometimes thousands of people are seized by a frenzy of dancing, without any cause or plausible motivation, a frenzy which they are unable to control and which only total physical exhaustion ends. The collective phenomenon manifests itself in public places, squares, fairs, streets, large areas of the community. Since the 12th century, when has been recorded the strange episode of the children that traveled the 20 kilometers of 20 the road between Erfurt and Arnstadt, to that of the collapse of the bridge over the Meuse, under the tremors amplified by the staggered dance of the over 200 people, to the episodes of Aachen, Metz, Strasbourg, Utrecht, Zurich or Basel, which take us to the end of the 16th century. As usual, the explanation of the phenomenon is at best uncertain. Modern psychology makes it part of a class that is difficult to diagnose and assess, under the tag 'mass psychogenetic diseases (MPI). Collective delusions, generated by the loss of the logical and critical control on the benchmarks of reality, in particular under the pressure of induced fear, panic, acute tension or maintained over long periods of time, in connection to a clear or unclear danger. Specialized literature quotes mas hysteria or epidemic hysteria, a phenomenon that Jung himself researched as one of the forms with severe consequences. The phenomenons of loss of collective control on the contact and interaction with reality are however not just part of our ancient history, but also that of our recent, contemporary one. Psychological disturbances can go as far as having large groups of people showing symptoms of some diseases, that should have a biological cause, but which upon careful medical research, proves non-existent. The symptoms seem to be sent through oral or visual contagion.
