 This study is designed to test the hypothesis that a single administration of intranasal oxytocin within 6 hours post-trauma facilitates the physiological recovery for the trauma, thereby preventing the development of Post Traumatic Stress Disorder PTSD in the months following the event. In the absence of such treatment i.e., under placebo conditions, we hypothesize that a greater proportion of persons will develop PTSD i.e., fail to recover from acute effects. 