From WikiLectures

Concussion or concussion is a reversible functional disorder, when a loss of consciousness of varying duration (from seconds to minutes) is most often caused by a direct or, more rarely, transmitted blow to the head. After regaining consciousness, the clinical findings are normal, dominated by headache and amnesia for the duration of the loss of consciousness, depending on the severity of the coma, usually retrograde amnesia (for the period preceding the injury) and possibly also anterograde (for the following period). A long-term complication can be non-specific post-convulsion problems (headache, photophobia, sleep disorders, anxiety, depression etc.) – these problems can be a manifestation of functional axonal impairment.