Athletes who take a serious blow to the head during competition shouldn't just shake it off and get back in the game. New guidelines advise them to see a physician immediately and refrain from play the rest of the day if they become unconscious or have persistent symptoms.
Common symptoms of concussion following head trauma, which is defined as an alteration of cerebral function, include headache, dizziness, nausea, vomiting, brief loss of consciousness, vertigo, light-headedness, amnesia, and difficulty concentrating. If symptoms last more than 15 minutes, the guidelines say athletes should be monitored for up to a week and return to competition gradually. If symptoms worsen, they should seek emergency treatment.
Voelker R. Caution for Concussion. JAMA. 1999;282(20):1908. doi:10.1001/jama.282.20.1908-JQU90009-3-1