According to a new study, over a third of people are walking around with the symptoms of a concussion. However, the symptoms are not actually caused by a concussion. Researchers say the concussion-like state of confusion is caused by stress and lack of sleep.

A survey of more than 31,000 people shows that insufficient sleep, mental health problems, and stress were the causes of symptoms that doctors are used to seeing in head injuries. Doctors refer to such symptoms as post-concussion syndrome (PCS) and they include headaches, dizziness, anxiety, insomnia, lack of focus, and memory loss.

27 percent of people in the survey reported having more than one of these symptoms. Between half and three-quarters of participants say they experience at least one. The most common of the symptoms are fatigue, lack of energy, and drowsiness. The researchers believe these numbers are actually higher in the general population.

The National Collegiate Athleetic Association and the US military funded the study. It was intended to improve care for athletes and soldiers who suffered from concussions. The survey consisted of 2,039 military service academy cadets and 18,548 student athletes.

“The numbers were high, and were consistent with previous research in this area, but it is quite shocking,” lead author of the study Dr. Jaclyn Caccese said. Dr. Caccese is also an assistant professor in The Ohio State University School of Health and Rehabilitation Sciences. She continued, “These are elite athletes who are physically fit, and they are experiencing that many symptoms commonly reported following concussion. So looking across the general population, they’d probably have even more.”

“When a patient comes into a clinic and they are a month or more out from their most recent concussion, we need to know what symptoms they were experiencing before their concussion to know if their symptoms are attributable to their concussion or something else,” Caccese explained. “Then we can start treating the concussion-related symptoms to hopefully help people recover more quickly.”

Trouble sleeping and mental health problems had the strongest links to the concussion-like symptoms. However, struggling in school, headaches, ADHD, and depression were also linked to PCS symptoms.

“Perhaps we can create a battery of symptoms more specific to concussion,” Caccese suggested. “This hopefully not only shows clinicians that we need to consider how people would have presented before injury, but also provides some normative data so they can interpret other patients. We really don’t know a lot about why people have persistent symptoms, and it seems to be very variable. So we’re trying to understand this better to help predict who will have a prolonged recovery, and who will not.”