"You know how a bell vibrates? That's how my brain was going at that time," he said. "I think five minutes later, I came back to myself. I went back out there and played football."

What Cartwright never did when the hit happened? He never told Washington's medical staff his head ached.

He's not alone. Thirty of 160 NFL players surveyed by The from Nov. 2-15 replied that they have hidden or played down the effects of a concussion.