Post-traumatic stress disorder (PTSD) is a set of mental health reactions that can develop in people who have experienced or witnessed a threatening event in their life or in the lives of people around them. The traumatic event can be a serious road accident, physical or sexual assault, war-related events or natural disasters. PTSD can develop immediately after the traumatic event or can develop weeks, months or even years later. PTSD is estimated to affect about 1 in every 3 people who have a traumatic experience. PTSD can be successfully treated and it depends on the severity of symptoms and how soon they occur after the traumatic event. The treatments include psychological treatments and antidepressant medication.