Throughout much of her young adult life, Terry Hatcher was living in a disassociated state, disconnected from the world -- zoned out. She tried to commit suicide at age 21.

It wasn't until she was 30 that the Oakland, Calif., resident learned she was suffering from an acute form of , or . As a child, she was abused for years by her bipolar mother -- hit with belts and other objects for any minor offense -- and the effects stayed with her.

"(The diagnosis) hit me like a ton of bricks," says Hatcher, who is a psychologist. "People with PTSD can't see a future. I thought either I will find someone to talk to about this, or I am going to die."

According to the Diagnostic and Statistical Manual of Mental Disorders, a reference used by the American Psychiatric Association that includes all currently recognized , 8 percent of the American population suffers from some form of PTSD, though experts in the field say up to 15 percent of Americans do. Although soldiers returning from war are more commonly known sufferers of PTSD, once called "shell shock" and "battle fatigue," PTSD can affect anyone who has suffered a traumatic event.

This includes witnesses of trauma, like the concertgoers who saw the suicide at the Swell Season performance last month at the Mountain Winery in Saratoga, as well as those whose lives were directly threatened by crime or accidents, like the residents of San Bruno, Calif., who were rocked by a massive PG&E gas explosion this month. Even experiencing a minor car accident can pull some people into the downward spiral of PTSD.

"Basically, PTSD can occur in many, many people when exposed to severe stress," says Dr. George Hamilton, a psychiatrist for Contra Costa Mental Health Services in Martinez, Calif. "It doesn't have to be war. It can be any kind of other event, like a natural disaster, where suddenly your world is turned upside down and certainly your life is at risk."

Nearly one-third of all victims of sexual assault develop PTSD sometime during their lifetimes, according to a National Women's Study released a decade ago, and many children suffer PTSD after being victims of sexual or physical abuse or neglect.

Unlike many mental disorders, PTSD has a specific diagnosis, and symptoms are relatively common across the board. Casey Taft, a psychologist at the National Center for PTSD at the VA Boston Healthcare System, calls the diagnosis of PTSD a "Chinese menu" of sorts.

In order to be diagnosed with the ailment, you have to first suffer from an event that causes trauma, one that threatens your life or your well-being directly or gives you the perception that your life is threatened. Next, you have to have three different symptoms of avoidance. People suffering from PTSD often isolate, dissociate or feel a sense of a foreshortened future. For Hatcher, she never thought she'd get married, have children or live a normal life.

Then, a PTSD sufferer must have two arousal symptoms, such as nightmares, a strong startle reflex, hypervigilance to threats of danger, anger, irritability or concentration problems. Many sufferers wake up multiple times at night or don't get very much sleep at all. Hamilton says common nightmares relive the trauma or come through in chase dreams or falling dreams, situations where the person is out of control.

Finally, these symptoms must show for 30 days or more and affect a person's daily life, whether it be relationships or job functioning. Sometimes, the symptoms of PTSD can be latent for months or years after the trauma.

"Some people may be having problems with anger, irritability and aggression," Taft says. "And others have these emotional numbing symptoms where they have trouble getting close to people."

It is important to note, however, that not everyone who experiences trauma will develop PTSD. Virginia psychologist Mary Beth Williams, author of several books on healing from the disorder, says some victims who survived the San Bruno fire may feel stress and nothing else while others may develop PTSD.

"Most people in the U.S. have been exposed to a traumatic event at one time or another," she says, noting that many people complained of suffering from trauma after the Sept. 11 terrorist attacks. "What makes some more hearty and others not is what we're looking at right now."

Michele Rosenthal, proprietor of www.healmyptsd.com, says she was living with an enormous amount of fear as a young adult. The Florida resident constantly scanned her environment for threats, and suffered from insomnia, nightmares and flashbacks. This behavior became routine after she had a near-fatal reaction to an antibiotic at age 13, one that melted away her skin.

"You get stuck in the fight, flight or freeze mode, and I never came out of the freeze mode," the 42-year-old says. "You're in so much pain that you will do anything to have it taken away."

Rosenthal was seeing a therapist when she started researching trauma and dissociation on her own around age 33. Through her research, she found that PTSD fit her symptoms, and the diagnosis was confirmed by her therapist.

She says PTSD is not something someone can just "get over," a pull-on-the-bootstraps disorder that eventually goes away on its own. Family and friends of someone who needs help may not recognize it at first.

"From the outside, it can look like the person with PTSD is giving in or not trying or just won't let it go," she says. "But if you understand PTSD, you may be able to help your loved ones."

Yet, many people don't get help. Sufferers who ignore the symptoms can ruin personal relationships, lose jobs, experience trauma-related disorders such as fibromyalgia, diabetes II, chronic fatigue and irritable bowel syndrome. Others may turn to drugs or alcohol to numb their feelings.

"We deal with all kinds of difficulties, changes and feelings, and commonly drugs and alcohol will go ahead and take those feelings away for a while," Hamilton says. "Part of the belief system is, 'You can't possibly understand what I've been through.' It's not true but that's how it feels."

While symptoms of PTSD are common, treatments of the disorder are varied and are not one-size-fits all.

Hatcher found that art therapy and talk therapy helped her through PTSD. Rosenthal says hypnosis worked for her. Some doctors and sufferers believe that PTSD can be cured through different forms of therapy, while others say it is a lifelong disorder.

Taft says the most important action a sufferer can take is to talk to someone about his or her feelings. It's a difficult request, he says, because part of PTSD is not wanting to talk about the trauma.

"It's really important to not avoid dealing with the trauma and working through it," he says. He adds that cognitive processing therapy, which helps you learn how going through a trauma changed the way you look at the world, yourself and others is effective. Exposure therapy, where the person is exposed to aspects of the trauma with the therapist present, has also been shown to help victims of PTSD. For example, a member of the audience at the Swell Season concert could return to the concert venue for therapy. Eye Movement Desensitization and Reprocessing (EMDR), an eight-phase method, is also shown to be effective in treating trauma.

Hamilton says that some medications can help a sleepless sufferer get rest, but support groups for trauma survivors, even Alcoholics Anonymous, will likely provide the most relief.

"It's possible to heal," he says. "What we're dealing with in all of these cases of PTSD are survivors. They've already gotten through it. And every time you cut yourself, there will be a scar. Some wounds don't heal, but others need some help healing."