Post Traumatic Stress Disorder (PTSD) is an anxiety disorder that develops in response to a traumatic event and that can significantly affect one's daily functioning. Experiencing or witnessing an event that causes intense fear, helplessness or horror can result in PTSD. Most people who experience traumatic events have brief adjustment periods during which they successfully cope with the experiences. For others, anxiety symptoms worsen over time and last for months or years, disrupting one's ability to function in everyday life.