Heidegger claims that Freud had to invent the “unconscious” in order to create a causal link between our conscious (thoughtful) actions and our animal urges, which for Freud were principally libidinal and erogenous.
Žižek claims that the unconscious represents “cuts” in the causal continuity: our trauma or PTSD is a division of causality (the trauma breaks our causal understanding). This requires a fantasy to stitch continuity back together so we may continue in the world.
The insight is to realize that the “disturbed” need a fantasy, a story. (And we are all disturbed.) However, the libidinal animal spirit has always offered a “normal” remapping of trauma, but it fell out of fashion.
The fantasy is the unconscious. Freud provided a name and categorization (psychologizing) that provides a quasi-scientific framework. This mythic scaffolding allows us to normalize the premodern human condition (animalism) in a modern (rational) way.