Approximately 14% of strokes happen when individuals are asleep, which represents about 58,000 emergency room visits annually, new research indicates.

Researchers at the University of Cincinnati reviewed the medical records of 1,854 adults who were treated in emergency rooms for ischemic strokes in a one-year period, HealthDay News reports. Fourteen percent of these patients, or 273 people in the study, woke up with stroke symptoms. According to the researchers, 98 of these patients would have been eligible for the clot-busting drug tPA if physicians had been able to pinpoint when the stroke started. If a stroke starts more than a few hours before a patient seeks treatment, tPA can cause bleeding that will extend and enlarge the stroke instead of helping, investigators said. Scientists are currently working on imaging studies to help determine which patients are most likely to benefit from tPA.

Until then, physicians are encouraging people to be more aware of symptoms that indicate a stroke. They say that if a person wakes up with symptoms, they should not wait for them to pass on their own.

“They should seek medical attention immediately. Even though tPA may not be an option in wake-up strokes, there are many other treatments that can be given in an emergency room or hospital,” said researcher Dr. Byron K. Lee, M.D.

Symptoms can include weakness on one side of the face, sudden vision problems, slurred speech, sudden severe headaches and sudden confusion according to the National Stroke Association. The study was published in the May 10 issue of the journal Neurology.