…But what if it’s a giant UFO, and I was in denial of it because I didn’t want my friend to panic?
Folie à deux, or shared psychosis, is a psychiatric syndrome in which symptoms of a delusional belief and hallucinations are transmitted from one individual to another. The same syndrome shared by more than two people may be called folie à trois. Recent psychiatric classifications refer to the syndrome as shared psychotic disorder and induced delusional disorder in the ICD-10, although the research literature largely uses the original name.
Folie imposée is where a dominant person initially forms a delusional belief during a psychotic episode and imposes it on another person or persons with the assumption that the secondary person might not have become deluded if left to his or her own devices. If the parties are admitted to hospital separately, then the delusions in the person with the induced beliefs usually resolve without the need of medication.
Folie simultanée describes either the situation where two people considered to suffer independently from psychosis influence the content of each other’s delusions so they become identical or strikingly similar, or one in which two people “morbidly predisposed” to delusional psychosis mutually trigger symptoms in each other.