Digital mental health platforms increasingly incorporate body-based therapeutic approaches, yet no standardized ontology exists for representing somatic experience computationally. This paper introduces the Cathexis Somatic Ontology (CSO), a formal vocabulary and relational schema for encoding body-based therapeutic data. The CSO defines entity classes for anatomical zones (29 zones with clinical significance rationale), sensation qualities (20 phenomenological descriptors), neurobiological organization patterns (16 territories derived from predictive processing, primary affect systems, and somatic marker theory), therapeutic change mechanisms (3 memory-system-based pathways), and intervention architectures (7 mechanism types). Entities are organized within a Markov blanket framework comprising four components (internal states, external states, sensory states, and active states), providing a principled computational structure derived from Friston's free energy principle. The ontology is grounded in seven major research programs: constructed emotion theory (Barrett), predictive processing (Friston), affective neuroscience (Panksepp), somatic markers (Damasio), neuropsychoanalysis (Solms), the entangled brain framework (Pessoa), and memory systems (Kandel, Nader, Schiller, Ecker). New to this version, Pessoa's work on combinatorial brain organization provides the architectural foundation for how the CSO represents distributed neural activation. Version 2.0 introduces a trifecta visualization architecture: three complementary rendering surfaces (BRAIN, BODY, WORLD) that correspond to the Markov blanket's internal, sensory, and external state components, sharing a unified rendering engine and visual language. Machine-readable representations (OWL, JSON-LD, Turtle) accompany CSO v1.1 as supplementary files.