Millions of people suffer from anxiety disorders, including posttraumatic stress disorder (PTSD)-a condition that can profoundly disrupt daily life. Although treatments like therapy and medication help many, there is still a major need for more effective and faster-acting options. In recent studies, a procedure called cervical sympathetic block (CSB)-an injection near a nerve cluster in the neck-has shown promise in reducing PTSD symptoms, as measured by standardized tools like the CAPS (Clinician-Administered PTSD Scale). In this study, the investigators will conduct a double-blind, randomized controlled trial comparing CSB to a sham (placebo) injection in patients with PTSD. The investigators will assess changes in PTSD symptoms and also monitor physiological markers (like pupil response, temperature, and heart rate variability) to better understand how the treatment works and to improve the precision of future therapies.