Concussions are known as "Minor Traumatic Brain Injuries." Though the brain often appears normal after brain imaging, most physicians believe there exists some amount of damage which would explain the confusion, headaches, double vision, nausea, vomiting, mood changes, inability to concentrate and amnesia that often occurs in these patients. Most patients with concussions recover by day 3 and any recurring headaches often resolve by the 3rd week. However, any vomiting, change in mental status, confusion, and sudden drowsiness after the concussion may suggest serious brain injury and the patient should receive prompt medical attention.
A review of the available medical literature reviews several different guidelines regarding the return to full athletic participation. But the general consensus is to err on caution and those patients whose functionality has not returned to baseline and continue to experience symptoms should not return to full athletic participation. For minor concussions without residual symptoms, we generally recommend 1 week of rest with gradual return to athletic participation if the patient remains asymptomatic and tolerates minor exercise (such as jogging).
One of the newest guidelines for high school atheletes experiencing concussions came out 2009 from the National Federation of State High School Associations as detailed here on the New Hampshire Interscholastic Athletic Association website:
http://nhiaa.org/PDFs/3076/SuggestedGuidelinesforManagementofConcussioninSports.pdf