Crowd behavior

‘Folie à plusieurs’ a term that describes a shared psychotic disorder - also known as "the madness of several."
Several people become swept up by a delusional idea, and this may have violent consequences in politics.
When this occurs in families, it is called 'folie en famille.'
Folie à plusieurs is a mass hysteria characterized by delusion. The line between mass hysteria and folie à plusieurs is not always very clear.
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Reference: ==
1.) https://journals.sagepub.com/doi/abs/10.1177/0957154X08094236