A minimal model of PTSD susceptibility and timescales.

Post-traumatic stress disorder (PTSD) is a debilitating condition characterized by intrusive memories, hyperarousal, and avoidance. Treatment outcomes vary, and mechanistic understanding remains incomplete. After trauma, only a minority (10-20%) develop chronic symptoms, while others recover over varying timescales. We present a minimal mathematical model using an autocatalytic symptom driver balanced by removal, capturing PTSD's bistability - a persistent switch to a high-symptom state after trauma. Individual susceptibility is determined by a single "resilience" parameter R, such that PTSD occurs only at low R. The model explains the broad distribution of recovery timescales at intermediate R (dynamical ghost). It also predicts that treatment must surpass a threshold to produce lasting improvement, consistent with clinical observations. We validate the model against longitudinal symptom data across multiple cohorts and trauma types.This simplified framework links physiology to trauma response dynamics and may help guide individualized treatment.