[1] In terms of Hegelian dialectics the conflict between the theoretical abstraction and its empirical negation (through trial and error) is resolved by a concretion of the two ideas, representing a theoretical abstraction taking into account the previous contradiction, whereupon the mediator vanishes.
A conceptual deadlock exists until the resulting hysteric breakdown precipitates some kind of resolution, therefore the Hysteria is a vanishing mediator in this case.
[3] Fredric Jameson introduced the term in a 1973 essay ("The Vanishing Mediator: Narrative Structure in Max Weber," in New German Critique 1 [Winter, 1973]: 52-89).
Alain Badiou uses a similar, but more explicitly post-structuralist term (″terme évanouissant″ or ″vanishing term″) in Théorie du sujet.
[1] Applications of this concept exist in various fields, making it a viable framework in cultural studies, literature, and qualitative research among others ("Developing the Vanishing Mediator as Theoretical Framework: Synthesis and Application," [Fall, 2019]).