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If you've lived through a frightening event, such as a car crash or an earthquake, it's normal to feel shocked and anxious. And you may have trouble sleeping.

But if these feelings keep you from getting on with your life and they don't start to fade away within a month, you may have post-traumatic stress disorder (PTSD).

If you have PTSD, you may keep replaying the event in your mind and go out of your way to avoid anything that might trigger memories of it.

If you think you have it, talk with your doctor as soon as you can. The sooner you get help, the more likely you are to feel better.

• It's normal to feel shocked and upset if something frightening has happened to you.
• But if these feelings don't fade within a month and you can't get on with your life, you may have PTSD.
• If you think you could have PTSD, it's important to get treatment right away. Early treatment can help to prevent PTSD. But it's never too late to get treatment.
• About 5 million Americans between the ages of 18 and 54 have PTSD.¹
• Children can get PTSD too. And it's just as important for them to get treatment as it is for adults. (To find out more, see Children and PTSD.)

People often think that you only get PTSD if you've survived something terrifying, like a rape or a war. But you can also get it if someone close to you dies suddenly or if you've been told you have a serious illness.

Sometimes people who witness disasters get PTSD.²

It's normal to feel frightened or anxious after something life-threatening happens to you, such as being in a plane crash or a flood. And it's normal to feel edgy and to have trouble sleeping. Having nightmares may also be part of getting over what's happened.³ And you may not want to talk about what you've been through.

Although these feelings are upsetting, they usually fade after a few weeks.³

But if these feelings last for longer than a month, and if they keep you from getting on with your life, then you may need help.⁴ It's important to talk with your doctor right away, because early treatment can help to prevent PTSD.

The difference between PTSD and other feelings you might have after a frightening or stressful event is that PTSD keeps you from living a normal life. If you have PTSD you may:⁴

• Keep replaying the event in your mind
• Suddenly feel like you are going through the event all over again
• Avoid things that may make you think about what happened
• Have a hard time concentrating
• Have a hard time getting along with people
• Have a hard time relaxing
• Have a hard time sleeping
• Feel very nervous all the time.

If you have symptoms like these for at least two days in the first month after you've been through a frightening event, your doctor may say that you have acute stress disorder.⁴

The symptoms of acute stress disorder are similar to PTSD. But if you have this disorder, you're especially likely to feel as if you're in a daze or feel numb. You may find that you don't enjoy doing things that you usually like to do.⁴

If you think you have acute stress disorder, it is important to get help as soon as possible. Sometimes, people who have acute stress disorder can go on to get PTSD.³ But getting treatment early may help you keep from getting PTSD.

You may not get PTSD right away. Some people don't get it until months or years later, but this is less common.³ It's more likely to happen if you felt lonely or if you didn't get much emotional support from your friends or family right after the event.

Children can get PTSD too. And if they don't get treatment, it can cause serious problems for them even once they grow up. It's much better for them to get treatment sooner rather than later. To find out more, see Children and PTSD.

PTSD is caused by different things in different people. And it is often caused by a combination of things.

Some of the events that are most commonly linked with PTSD are:

• Car accidents
• Plane crashes
• Natural disasters, such as earthquakes or floods
• Assaults
• Rapes
• Terrorist attacks
• Being involved in a war.

Some of these events are more likely to cause PTSD than others. For example, you are more likely to get PTSD if you are raped or see a terrorist attack than if you are in a car accident or someone close to you dies suddenly.²

Even still, 4 in 10 people with PTSD will have gotten it because someone close to them died suddenly.²

Some doctors think that you get PTSD because an event is so shocking that your brain can't cope with the stress.²

Some people with PTSD have abnormal levels of chemicals called hormones in their brain long after they've been through a traumatic event.⁵ Researchers think that the event may upset the balance of chemicals in your brain. But we don't know for sure whether this causes PTSD, or is the result of having PTSD.³

Not everyone who lives through a frightening event gets PTSD.³ And we don't know why some people get it and others don't.

But there are some things that make it more likely that you will get PTSD. These things are called risk factors. For example, if you were depressed before you went through an upsetting event or if you didn't get much support from your friends or family afterward, then you may be more likely to get PTSD.

It's important to remember that even if you have a risk factor and live through a frightening event, it doesn't mean you will definitely get PTSD.

To find out more, see Risk factors for PTSD.

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.