This study tests whether psilocybin (a psychedelic compound) combined with intensive therapy can help treat chronic PTSD better than therapy alone. Fifteen patients with PTSD will receive one dose of psilocybin alongside 12 therapy sessions completed over a single week. Researchers will track feasibility, safety, symptom improvements, and use wearable devices to monitor physiological changes. The results will help determine whether larger trials should test this innovative combination therapy.