When something traumatic happens—you suddenly lose a loved one, get into a car crash, or witness a terrorist attack—it’s natural to be extremely upset and even feel physically ill. Your “fight or flight” response kicks in, flooding your body with stress hormones that leave you jittery and on edge. You might have nightmares about the event or break down in tears when you see or hear something that reminds you of it.

That’s post-traumatic stress (PTS), and it’s not a disorder—at least not yet. “PTS is considered a normal reaction to stress and not a mental illness,” Sanam Hafeez, PsyD, a neuropsychologist and teaching faculty member at Columbia University, tells Health.

She explains that PTS is common and usually resolves on its own. “Say you barely avoided an accident on a road infamous for being dangerous. You may avoid that road and alter your route. You may even feel nervous about driving down a similar road. You may later dream about the accident you avoided. But after a few days, these thoughts subside then eventually fade.

Most of the time, that’s exactly what happens: A stressful event occurs, it shakes you up, but within a few days or weeks it’s no longer a major issue. No treatment is necessary, though anything that helps you relax—deep breathing, yoga, painting, exercise—might help you feel better and move the process along.

Post-traumatic stress disorder (PTSD), however, is different.

PTSD doesn’t go away so quickly, and your usual de-stressing techniques aren’t sufficient to help you feel better. Instead, you remain incredibly anxious, relive the incident over and over in your mind, avoid anything that might trigger your memory of it, and remain on high alert for danger.

If you have these symptoms for at least one month and they’re bad enough that they interfere with your everyday life, then you might have PTSD. The symptoms can start immediately following a trauma, or they might first appear months or years later, according to the PTSD Alliance, a national advocacy organization.

One common misconception, says Dr Hafeez, is that PTSD only happens to combat veterans. While it’s true that the disorder is prevalent among soldiers—up to 30% of people in active war zones later develop it—it’s also fairly common in the general population. An estimated 8% of all Americans have PTSD, and women are twice as likely as men to be affected by this anxiety disorder. “It can occur in anyone exposed to a terrifying traumatic event, regardless of age or background,” says Dr Hafeez.

Is it PTSD?

Only a trained mental health expert can diagnose PTSD, and the duration of your symptoms is only part of the picture. “The American Psychiatric Association defines it as a psychiatric disorder that can occur in people who have experienced or witnessed a traumatic event such as a natural disaster, a serious accident, a terrorist act, war/combat, rape, or other violent personal assault,” says Dr Hafeez.

In order to be diagnosed with it, a person must have “prolonged disturbing thoughts that interfere with their normal daily lives,” says Dr Hafeez. “They may have very vivid flashbacks that put them right back into the traumatic event as if it is happening again and again.”

Intense nightmares are very common, as is the tendency to disengage from friends and family. Someone with PTSD will be “incredibly avoidant of doing any activity that may remotely remind them of the trauma they experienced,” she adds. “They also can be triggered by loud noises, certain smells, sounds, or other reminders. They often say they feel jumpy and may seem very startled at the slightest touch.”

If you’re diagnosed with PTSD, therapy and/or medication will likely be in order. Sertraline (Zoloft) and paroxetine (Paxil), two antidepressant medications that are also commonly prescribed for anxiety, are FDA-approved specifically for PTSD.

There are several types of therapy that you can try, but prolonged exposure therapy and cognitive processing therapy are the most widely used and effective, says Dr Hafeeze. Prolonged exposure therapy involves working closely with a professional to review the trauma and your reaction to it until you learn to associate it with less distress. Cognitive processing therapy is a type of cognitive behavioural therapy designed to challenge your beliefs about the trauma and related triggers so you can improve your day-to-day functioning.

Most people require at least 12 to 15 weeks of therapy to treat PTSD, but sometimes the disorder remains chronic. That means you may need some type of treatment for the rest of your life in order to feel your best. If you suspect you have PTSD, the PTSD Alliance offers resources that can help you find treatment, as well as a list of hotlines and groups that can help you start your journey toward healing.