Post-traumatic stress disorder (PTSD) is a severe psychological reaction to a life-threatening trauma. It can also be provoked by threats to a person's physical integrity, prolonged stress such as torture or being a prisoner of war, or witnessing the death of a loved one. It involves anxiety, depression and specific features such as nightmares, flashbacks, hyper-arousal and avoidance behaviours. Psychiatric reactions can be provoked by various traumas including assault, rape, severe road traffic accidents, surviving a fire, surviving a terrorist incident, being mugged, or witnessing someone being badly injured or killed. Acute stress reactions involve feelings of intense anxiety, dizziness and feeling faint, numbness and detachment, and poor sleep. These occur in the first few hours after a trauma, may be self-limiting and may last just a few days. The estimated lifetime prevalence of PTSD among adults in the general population is about 7–10", with women twice as likely as men to have PTSD at some point in their lives.