Surprisingly, there’s been no observed correlation between a concussion’s severity and its sufferer’s chances of contracting what’s called “post-concussive syndrome.” If you’re one of the unlucky 15–20% who don’t recover right away, though, your symptoms can persist for weeks or even months after your injury — symptoms including chronic headaches, disorientation, ringing in the ears, anxiety, irritability, insomnia, and fatigue (via Brain Forest).

If you’re one of the really unlucky ones, though, your brain could simply start deteriorating later in life, even if you haven’t had any symptoms for years or decades. According to a study in Science, even injuries that leave no brain damage visible on an MRI scan can lead to debilitating symptoms as the sufferer ages, including impairments in judgment, learning, memory, and emotions. This sort of long-term, irreparable deterioration is why more than 4,500 retired football players sued the NFL early in the 2010s over the dementia, depression, and Alzheimer’s their careers had allegedly caused them. (They settled out of court.)

If you suffer a blow to the head, experts say the best way to avoid medium- and long-term consequences is to immediately seek medical attention and take it easy for a few days if you’re showing signs of a concussion (the Centers for Disease Control and Prevention has posted a helpful rubric). In other words, “Just shake it off and get back in the game” is about the worst possible advice, assuming you want to keep your brain intact.