Fainting, no matter why it happens, is the result of a short period of time when the brain’s blood supply is decreased, explains Lawrence Phillips, MD, an assistant professor of medicine in the cardiology division at New York University’s Langone Medical Center. “The cause can stem from many different parts of the body, including a person’s blood pressure going down, heart rate going down, and from neurologic reasons independent of the heart,” he says. “We try to find out why the blood pressure or heart rate would go down. Some of these reasons are common and not worrisome, but others need more evaluation.”
Even if you don’t faint from it, that drop in blood pressure or heart rate can cause lightheadedness, that very specific yet hard to describe feeling that you might pass out. (Dizziness, on the other hand, can include lightheadedness, but it also comes with the feeling that the room is spinning around you.)
It’s tricky to know when fainting or lightheadedness is a cause for concern—even doctors often feel stumped, which is why Thiruganasambandamoorthy has developed a screening tool that could help predict whether or not a person who has fainted is likely to have an underlying health problem. Below, 9 potential causes. And no matter what, play it safe by seeking medical attention for any new symptoms, or ones that don’t resolve themselves.