It is what we don’t know about concussions that is as scary as what we do.

No one is exactly sure what happens to the brain when you suffer a concussion like the one that left Brian Westbrook motionless on the turf in Washington a few weeks ago.

What is known is that doctors speak in grave terms when a concussion leaves someone out cold, as happened to Westbrook.

No doubt we will be hearing a lot of concussions again this week because of what happened to Westbrook in D.C., what happened since, and what happened yesterday in San Diego. Westbrook left the game after a single series in the second half. The diagnosis? Another concussion.

Westbrook was cleared by the Eagles medical staff to play against the Chargers. Actually, he had been cleared to play the Sunday before against the Cowboys. But when he developed headache symptoms late Friday afternoon, he was scratched from that game.

Not everyone agreed with the decision to allow Westbrook back on the field yesterday. Even the medical opinions are split.

The NFL has been looking into the issue of concussions and how teams handle them.

No doubt they will review the Westbrook case.

The team is now indicating they will take every precaution with Westbrook.

The whole thing brings up bad memories of another local superstar, Eric Lindros, and the concussions that cut his career short.

One of the things that is not known is just how susceptible you are to another concussion after suffering an initial one.

What is known is this: Don’t look for Brian Westbrook to be back on the field any time soon.