The concept of PTSD has been with us for centuries but has had many names. It was “shell shock” and “battle fatigue” before it was PTSD and is now known to affect not just military veterans but anyone who has gone through an intense traumatic experience. In fact, about one in 11 people will have in their lifetime, according to the American Psychiatric Association.

While are a huge part of PTSD, they’re not the whole picture. People with PTSD often suffer from, negative thoughts, and impulsive or self-destructive behaviour as well.

PTSD also has its own treatments, which is why it’s important to get the right diagnosis.

“With proper treatment, veterans and all Americans can lead happy, whole, healthy lives with PTSD,” says Emily Blair, manager of military and veterans’ policy at the National Alliance on Mental Illness. Here are the signs and symptoms to watch for.

Experiencing or Witnessing A Life-Threatening Event

PTSD can strike anyone who has gone through a life-threatening event. That means not just war, but sexual assault, natural disasters like earthquakes or hurricanes, mass shootings, motor vehicle accidents, and more.

“There has to be exposure to some sort of very extreme type of horrible event,” says Jack Nitschke, PhD, associate professor of psychiatry and psychology at the University of Wisconsin School of Medicine and Public Health. “Something has to happen in the external world.”

Not everyone who has gone through trauma will develop PTSD. Alternately, for some people, learning about violence or tragedy that happened to someone else–like the murder of a family member or friend–can lead to the disorder.

Flashbacks

Flashbacks and unwanted, intrusive memories are known as “re-experiencing symptoms,” which can make a trauma survivor feel like they are reliving the traumatic event. Smells, sights, and sounds–like a car backfiring, the whirring of a helicopter, or a news report–can all trigger flashbacks.

“Those [triggers] go to the deep part of your brain. Your instincts take over,” says Elspeth Cameron Ritchie, MD, MPH, a retired military psychiatrist.

NightMares

Flashbacks are among the best-known symptoms of PTSD but nightmares–one of many reasons people with PTSD often have poor sleep–are actually more common. Nightmares or upsetting dreams about the traumatic event are also considered re-experiencing symptoms since they can make people with PTSD feel like they are back in the time and place of their trauma. Nightmares and other re-experiencing symptoms can sometimes be triggered by a person’s own thoughts or certain words.

Avoiding People, Places, or Things

Many people with PTSD go out of their way to avoid anything that reminds them of the original trauma or could be a trigger. For example, someone with PTSD might stop driving after a car accident or avoid watching movies about hurricanes if they’ve been through one.

This avoidance can become broader than a specific person or setting, says Nitschke. “If someone has been a victim of sexual assault, not only do they avoid that person who might still be at their university, but they might avoid men altogether, avoid going to classes,” he says. “They become immobilized.”

In some cases, avoidance takes the form of emotional numbing. Some people with PTSD might refuse to think or talk about the trauma, instead finding distractions in activities or alcohol or drugs, according to the American Psychological Association.

Been Constantly On The Lookout For Threats

This PTSD symptom is called hypervigilance. “You’re scanning the environment all the time,” says Dr. Ritchie, or on high alert constantly.

That might mean always sitting with your back to the wall in restaurants or lecture halls so you can see everyone and everything taking place in front of you. “They don’t want anyone sneaking behind them,” says Sonya Norman, PhD, director of the PTSD consultation program at the National Center for PTSD and psychiatry professor at the University of California San Diego. “They want to be ready to respond.”

Like nightmares, this heightened awareness can contribute to sleep problems in people with PTSD. Falling asleep and staying asleep can be more difficult if any small noise or change wakes you up.

Getting Startled Easily

This symptom, sometimes called hyperarousal, is closely related to hypervigilance. People with PTSD often have an exaggerated reaction when they’re surprised or startled, especially if the intrusion–a sound, smell, noise, or sight–reminds them of the original trauma.

“Somebody comes up close behind you and you jump a mile,” Nitschke explains. “Before the trauma, you wouldn’t have. Hyperarousal can interfere with sleep and concentration, and it may also come out as outbursts of anger, he adds.

Startling easily is a distinctive feature of PTSD; it’s not such a prominent symptom of other anxiety-related disorders.

Depression or Irritability

Since 2013, the diagnostic criteria for PTSD have included mood-related symptoms like depression, anger, guilt, shame, and hopelessness about the future. “These aren’t necessarily unique to PTSD, but I think there’s a change after the trauma,” says Norman. “Because of what they saw or what they did, or [because] they couldn’t save the day, they feel a lot of guilt. It’s very common to overestimate how much control they had and blame themselves.”

Those emotions can lead to negative beliefs about yourself, like “It was my fault” or “If I hadn’t taken that one drink,” Nitschke says.

Soldiers may feel prepared for some of what they experience in war, but no one is “prepared” for trauma like sexual assault. “[Sexual assault survivors] often feel very vulnerable and ashamed,” says Dr. Ritchie. “They feel that they have contributed to it in some way.”

Chronic Pain

Not everyone with PTSD has chronic pain, and not everyone with chronic pain has PTSD, but the two conditions do overlap. Between 15% and 35% of people with chronic pain also have PTSD, according to the U.S. Department of Veterans Affairs.

“We don’t fully understand the relationship,” says Norman. “Having your stress level in ‘turbo’ nonstop might just wear down your body after a while.”

The trauma itself can also cause pain: headaches from a brain injury, or back pain from a spinal injury, for example. But even removing physical causes from the equation, there does seem to be a higher level of chronic pain in people with PTSD than without. “This suggests that there [may be] some common neurobiological pathways,” says Norman. “We don’t know for sure.”