If you nearly drowned during your childhood, you may have a fear of water as an adult — the near death experience was so traumatic it still impacts your life. Traumatic memories from childhood could cause you to develop post-traumatic stress disorder (PTSD) in adulthood. 

But new research shows that you don't have to have a vivid memory of your trauma to develop PTSD. Your mind may subconsciously remember the fear that you experienced many years ago, even if you don’t recall any or very few of the details.

Dr. Andrew Poulos, a former University of California, Los Angeles, postdoctoral scholar, and his colleagues conducted a study to find out if some parts of early life memories still exist, and how they affect people later in life. For the study, the researchers used rodents to test their hypothesis. The juvenile rodents were placed in unpredictable new and stressful environments. The animals were tested later as adults to see if they remembered the stressful situations, and the researchers measured their levels of fear. Rodents that were exposed to the stressful environments showed more signs of anxiety and fear, the researchers found. 

“These heightened levels of fear and anxiety corresponded with drastic changes in daily rhythms of circulating hormone corticosterone,” Poulos said in a press release. Corticosterone is the hormone that controls your response to stress. In this experiment, researchers found that in the amygdala, the part of the brain that learns fear, corticosterone levels increased.

The researchers concluded that you don’t have to remember traumatic events to experience negative effects, such as fear and anxiety. According to Mayo Clinic, PTSD is a mental condition that is triggered by traumatic events you’ve experienced or witnessed. If you have constant flashbacks, nightmares, or severe anxiety, you could be suffering from the disorder.

According to the Department of Veterans Affairs, every year, 5.2 million adults suffer from PTSD. Victims of abuse, people with mental problems, or those who have suddenly lost loved ones are more prone to developing the disease. In urban communities, the condition is known controversially as the “hood disease.” Kids who have witnessed murders are also at risk for developing the disorder. “Youth living in inner cities show a higher prevalence of post-traumatic stress disorder than soldiers,” Dr. Howard Spivak, director of the Centers for Disease Control and Prevention’s Division of Violence Prevention, told CBS San Francisco

Overall, your past could be causing anxiety in your present-day life even though you don’t remember the exact event that triggered it. 

For people struggling with symptoms of PTSD, Mayo Clinic recommends psychotherapy combined with certain medications. Psychotherapy can be divided into several categories. For example, cognitive therapy helps PTSD patients recognize their thinking patterns, while exposure therapy uses virtual reality programs to allow you to re-enter the environment you were traumatized in. Sometimes, PTSD patients are also prescribed antidepressants or anti-anxiety medications to ease their symptoms.