A blow that causes a person to black out can also cause a concussion. However, someone could receive a concussion and not black out. In fact, according to UPMC Health Beat, over 90% of all concussions are not accompanied by a loss of consciousness, and a concussion accompanied by a knockout doesn’t automatically indicate a more serious injury or the necessity for a longer recovery period. In their 2011 study in which they analyzed symptoms following sports-related concussions in a sample of high school football players, just two out of 107 participants with longer recovery times reported a loss of consciousness under one minute. 

Thirty-four players who reported dizziness and 35 who reported headaches had long recovery times. Other signs and symptoms reported by those who had been concussed included confusion, post-traumatic or retrograde amnesia, imbalance, dizziness, vision problems, personality changes, fatigue, and vomiting. The International Concussion Society recommends seeing a doctor within a day or two of a head injury if concussion is suspected and notes that the American Academy of Pediatrics recommends calling a child’s doctor if they receive anything heavier than a light bump on the head. Concussion outcomes are reportedly generally positive when treated quickly.