Post-traumatic stress disorder is a kind of anxiety disorder. It can occur after you've seen or experienced a traumatic event that involved the threat of injury or death.

Post-traumatic stress disorder (PTSD) may occur soon after a major trauma, or it can be delayed for more than six months after the event. When it occurs soon after the trauma, it usually gets better after 3 months. However, some people have a longer-term form of PTSD, which can last for many years.

PTSD can occur at any age and can follow a natural disaster such as a flood or fire, or events such as war, a prison stay, assault, domestic abuse, or rape. The terrorist attacks of Sept. 11, 2001, in the U.S. may have caused PTSD in some people who were involved, in people who saw the disaster, and in people who lost relatives and friends. These kinds of events can produce stress in anyone, but not everyone develops PTSD.

We do not know what causes PTSD, but psychological, genetic, physical, and social factors are involved. PTSD changes the body’s response to stress by affecting stress hormones and chemicals that carry information between the nerves (neurotransmitters). Having been exposed to trauma in the past may increase the risk of PTSD.

Having good social support helps to protect against PTSD. In studies of Vietnam veterans, those with strong support systems were less likely to get PTSD than those without social support.

People with PTSD re-experience the event again and again in at least one of several ways. They may have frightening dreams and memories of the event, feel as though they are going through the experience again (flashbacks), or become very upset during anniversaries of the event.

Symptoms of PTSD fall into three main categories:

1. Repeated "reliving" of the event, which disturbs day-to-day activity

• Recurrent distressing memories of the event
• Repeated dreams of the event
• Flashback episodes, where the event seems to be happening again and again
• Physical reactions to situations that remind you of the traumatic event

2. Avoidance

• Inability to remember important aspects of the trauma
• Lack of interest in normal activities
• Feelings of detachment
• Sense of having no future
• Emotional "numbing", or feeling as though you don’t care about anything
• Less expression of moods
• Staying away from places, people, or objects that remind you of the event

3. Arousal

• Irritability or outbursts of anger
• Sleeping difficulties
• Difficulty concentrating
• Exaggerated response to things that startle you
• Excess awareness (hypervigilance)

You also might feel a sense of guilt about the event (including "survivor guilt"), and the following symptoms, which are typical of anxiety, stress, and tension:

• Paleness
• Feeling your heart beat in your chest (palpitations)
• Headache
• Fever
• Fainting
• Dizziness
• Agitation, or excitability

There are no tests that can be done to diagnose PTSD. The diagnosis is made based on a certain set of symptoms that continue after you've had extreme trauma. Your doctor will do psychiatric and physical exams to rule out other illnesses.