You can develop post-traumatic stress disorder when you go through, see or learn about an event involving actual or threatened death, serious injury or sexual violation.

Doctors aren't sure why some people get PTSD. As with most mental health problems, PTSD is probably caused by a complex mix of:

• Inherited mental health risks, such as an increased risk of anxiety and depression

• Life experiences, including the amount and severity of trauma you've gone through since early childhood

• Inherited aspects of your personality — often called your temperament

• The way your brain regulates the chemicals and hormones your body releases in response to stress