The United States' Centers for Disease Control and Prevention (CDC) defines post-traumatic stress disorder (PTSD) as an intense physical and emotional response to thoughts and reminders of the event that last for many weeks or months after the traumatic event. On World Mental Health Day 2021, Ritika Aggarwal, Consultant Psychologist at Jaslok Hospital and Research Centre in Mumbai, takes us through symptoms, causes and diagnosis of PTSD.