Cleveland Browns wide receiver Cedric Tillman (concussion) has now missed four games in a row due to an injury he picked up in Week 12 against the Pittsburgh Steelers. It's unusual to see players miss this much time due to concussions, but the brain isn't fully understood by medical science yet.Concussions are fickle injuries, and some can take far longer to recover from than others. NFL players come back before they're fully recovered typically, though. The brain isn't fully healed from this ...