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.

Treatment aims to reduce symptoms by encouraging you to recall the event, express your feelings, and gain some sense of control over the experience. In some cases, expressing grief helps to complete the necessary mourning process. Support groups, where people who have had similar experiences can share their feelings, are very helpful.

People with PTSD may need to treat depression, alcohol or substance abuse, or related medical conditions before addressing symptoms of PTSD. Behavioral therapy is used to treat avoidance symptoms. This can include being exposed to the object that triggers your symptoms until you become used to it and no longer avoid it (called graded exposure and flooding).

Medicines that act on the nervous system can help reduce anxiety and other symptoms of PTSD. Antidepressants, including selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine (Prozac), can be effective in treating PTSD. A doctor should monitor you if you take these drugs, because they can have side effects. Sedatives can help with sleep disturbance. Antianxiety medicines may be useful, but some types, such as benzodiazepines, can be addictive.

You can find more information about post-traumatic stress disorder and coping with a national tragedy from the American Psychiatric Association.

The best outcome, or prognosis, depends on how soon the symptoms develop after the trauma, and on how quickly you get diagnosed and treated.

• Depression, anxiety, and fear of things that are not usually frightening to other people (phobia), may be part of this disorder
• Alcohol abuse
• Drug abuse

Although traumatic events like the September 11 tragedy can cause distress, not all feelings of distress are symptoms of PTSD. You should talk about your feelings with friends and relatives. If your symptoms last longer, or are worse, than those of your friends, contact your doctor.

You should seek help immediately by going to the emergency room or calling the local emergency number (such as 911) if you feel overwhelmed by guilt, if you are impulsive, thinking of hurting yourself, unable to contain your behavior, or if you have other very distressing symptoms of PTSD.

You can also contact your doctor for help with ongoing problems such as recurrent thoughts, irritability, and problems with sleep.

Research into ways to prevent PTSD is ongoing.