Derealization — the phenomenological experience in which the external world loses its quality of ordinary reality, appearing strange, flat, dreamlike, or otherwise divested of its usual significance — occupies a precise and heavily theorized position within the depth-psychological corpus. The term appears most consistently in the trauma literature, where it is classified as a dissociative phenomenon co-occurring with depersonalization, amnesia, and identity fragmentation. Herman situates derealization within the broader architecture of traumatic constriction, describing how the world’s ordinary meanings become inaccessible under overwhelming threat. Lanius and colleagues advance a neurobiological account, linking the derealization subtype of dissociative PTSD to corticolimbic over-inhibition — specifically, heightened medial prefrontal and anterior cingulate activation suppressing limbic response. Siegel positions derealization within a taxonomy of clinical dissociation implicating disrupted integration of consciousness, perception, and identity. The pharmacological literature, cited by Herman, implicates κ-opioid receptor dysregulation and cortical associative pathway inactivation. Hillman’s archetypal psychology approaches adjacent territory through the concept of depersonalization as anima-loss, though derealization as such receives less direct attention in that lineage. A productive tension persists between phenomenological, neurobiological, and structural-dissociation accounts, making derealization an index concept for the wider debate about how mind, body, and world cohere under conditions of extreme threat.