Injuries like concussions are often heard of in pro-football, but what exactly is a concussion, and how is it treated?

FOX News Radio's Jennifer Keiper reports in the fourth installment of our ten-part series investigating the growing concern about concussions in the sport:

A concussion is a brain injury that is the result of the brain being shaken. Dr. Holly Benjamin, Director of Primary Care Sports Medicine at the University of Chicago says diagnosing it can be a challenge because it presents in many different ways, often headaches or dizziness.

(Benjamin) "Some kids even have amnesia where they don't really remember what happened at the time they got their head hit. And there's a whole list of other symptoms such as unusually excessive crying or feeling sad or even acting kind of silly."

Chris Nowinski played pro-football and moved onto WWE Wrestling, but after some hits his head started throbbing and when he tried to move around:

(Nowinski) "For some reason, for the first time in my life I couldn't remember things. The world was a confusing place."

Nowinski's career ended due to concussion.

Dr. Benjamin says every athlete who has a concussion has at least four times greater lifetime risk of having a second one. Treatment includes rest, physical and mental, and persistent symptoms should also be addressed, such as sleeping issues or emotional problems.

In Chicago, Jennifer Keiper, FOX News Radio.

CLICK HERE for more of the FOX News Radio series "Head Games: The Dark Side of Football".

CLICK HERE to listen to the full FOX News Radio special "Head Games: The Dark Side of Football".