Inside that hard skull of yours, the brain is a soft organ surrounded by spinal fluid. Normally, the fluid cushions your brain and keeps it from banging into your skull. But if your head or your body is hit unexpectedly hard, your brain can suddenly crash into your skull and temporarily stop working normally, bringing on a concussion.
There are many ways to get a concussion -- from fights, falls, playground injuries, car crashes and bike accidents. Concussions can also happen while participating in rough or high-speed sports, such as football, boxing, hockey, soccer, skiing or snowboarding.
They are "a very serious problem," said Rich Kaplan, a pediatrician with the Children's Hospital of Philadelphia Network. "For pediatricians, the whole focus is on prevention."
But concussions and head injuries occur because not all accidents can be prevented.
"If your child sustained a blow to their head, the following symptoms: headache, nausea, dizziness, vomiting, disorientation and confusion should prompt you to get on the phone with the primary care doctor or pediatrician to discuss what happened and the potential need for being seen," urged Kaplan.
Many doctors agree that a person who might have a concussion should immediately stop any kind of activity or sport. Resuming activity before the brain heals fully and returns to normal increases the person's risk of more serious brain injury.
A pattern of repeated concussions or a severe concussion may even cause long-lasting problems in speaking, movement or learning.
Said Kaplan: "Great concern exists amongst doctors for the individuals who participate in sports and wind up getting hurt. We're recognizing the impact as they get older."
Indeed, reports of concussions have pervaded broadcasts covering hard-hitting sports like hockey -- former Flyers captain Keith Primeau actually left the sport because of concussions -- and football.
A cumulative pattern of injury and the results that follow after repeated trauma to the head are especially dangerous for student athletes, when the brain is still developing.
A decision regarding when a child can return to sports is an important one. Whether a child has been injured previously will have bearing on the decision because it is known, studies have shown, that a second injury to the head after a first concussion is extremely dangerous.
Indeed, it has drawn the attention of Congress. Just two weeks ago, a bill supported by both parties targeted the need to bring down the concussion rate among high school football teams, with improvements called for in helmet construction.
The bill was put before Congress on what was "Brain Injury Awareness Day."
Cynthia Boyer has been working in this field for the past two decades. She serves as the senior clinical director of Brain Injury Services at Bancroft in Haddonfield, N.J.
"One of the biggest problems with concussions is the underreporting of symptoms by athletes," explained Boyer, with miild concussions, "the most difficult area to diagnose and treat because so many athletes become desensitized to symptoms over time, including headaches, ringing in the ears, sensitivity to light and difficulty perceiving sensory information."
There are no age barriers: "Concussions will just as likely disable young players as high school team members."
Added Boyer: "When a person does not have ample time for their brain to return to its proper balance, a second concussion, if it occurs, is implicated in causing serious long-term effects."
Although complex, the consequences of concussions are better understood. Some athletes become "used to" these symptoms. Others will cover them up to avoid letting their team down. Some don't want to miss any game time.
In all of these cases, experts agree that a zero-tolerance attitude must prevail. As Kaplan explained, "Everyone involved with the player must understand that this is in the best interest of the athlete."
Those treating concussions agree: Coaches, players, parents, and fans must abide by the rule that has trickled down from the major sporting leagues to playing fields all across America: "When in doubt, sit it out."