It doesn't take a hard hit.. The one to Brian Westbrook in the Eagles-Chargers game didn't look serious.
Westbrook even got up after as if nothing was wrong. But for someone who's had a previous concussion, it was enough.
A second concussion for Westbrook may shock fans, but not brain injury experts.
Dr. Rob Franks, of the Cooper Bone and Joint Institute, says, "Once someone has had a concussion, they are 4 to 6 times more likely to have another one."
And that can be weeks, or even years later.
Westbrook had one just 3 weeks ago, in a game again the Washington Redskins.
Then, he was laid-out on the field for several minutes, reportedly going in and out of consciousness.
Doctor Rob Franks of Cooper University Hospital says when someone gets a concussion, the brain cells are left shaking and twisting, and it can lead to permanent changes in the brain.
Concussions have been a growing concern for the National Football League, and other high contact sports.
I spoke with former Flyer Keith Primeau about the issue in May. His career was cut short due multiple concussions... the effects are still with him today.
"I sometimes get head pressure, fatigue, lethargy," says Primeau.
And another Flyer, Simon Gagne was also plagued by months of headaches after suffering several concussions at the end of the 2007 season.
A few weeks ago, Congress began looking at the problem, and questioning NFL commissioner Roger Goodell on steps the league is taking.
New helmets have been introduced with better shock-absorbing powers.
But Dr. Doug Smith, of the Penn Brain Injury Center says they may not help.
Dr. Smith says, "These are not based on any solid scientific data. Just putting more springy things in there doesn't necessarily make it any better."
After a concussion, experts now recommend total mental and physical rest.
Coach Andy Reid says that's a priority for Westbrook.
At his news conference today, Reid said.,"Number 1 is Brian's health, you can kind of put football aside, and make sure he's taken care of."
It's very difficult to say when an athlete is no longer at risk after a concussion. A battery of tests are used to look at reaction time and memory.
However it's possible athletes may never FULLY recover, and can always be at a greater risk for problems.
Two of their biggest risks are for depression, and early Alzheimer's disease.
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