Post-traumatic stress disorder (PTSD) is a psychiatric condition that can occur when you have lived through or witnessed a violent, life-threatening event. Veterans who have had traumatic combat experiences, such as seeing their comrades killed, may suffer the emotional effects long afterwards. PTSD symptoms are severe and disruptive to your life and relationships. You may re-live the trauma through flashbacks, be constantly anxious and on the alert, and feel detached or estranged from those around you. Psychosis, on the other hand, is not a response to a specific traumatic event. It develops out of a combination of biological, psychological, and environmental factors. Some people are genetically predisposed to psychosis. There is no clear, identifiable, single cause for psychosis. The symptoms, however, can be similar in some ways to PTSD. Psychosis sufferers experience hallucinations, and can be withdrawn and emotionally disengaged from everyone around them. Veterans with PTSD may display psychotic symptoms, including paranoia and delusions. PTSD can be treated with psychotherapy, medication, or a combination of both. Psychosis almost always requires medication, and psychotherapy by itself is not effective in relieving symptoms of psychosis.