Champ,

Kayley is half right. Once concussed means you will have less tolerance for a future impact like Kayley said but the part most people never hear is this: Your brain never fully heals to the pre-concussed state.

Many will feel like they have recovered fully but when their brain is put under stress, concussion symptoms will likely manifest again. The triggering stress can be a simple jarring with no head contact, a fever or other illness, school stresses like tests and exams, lack of sleep issues, spending time at altitude above 8000 feet or so, emotional stresses like a break-up or serious injury, etc.

Basically, the concussed brain has much less tolerance for the common stresses of life. Since these triggers may happen months or years later, the person often does not link them to the concussion.

One concussion expert suggests that all doctors include an entry in the patient's medical record that there is a possibility of a concussion if the trauma has even a remote likelihood of jarring the head. The IDC-9 code for this is 850.9. This enables doctors to understand symptoms that manifest later as possibly due to the previous injury.

Then there is the issue of sub-concussive impacts. The brain is much more sensitive to sub-concussive impacts after a previous full concussion.

Personally, I can give myself a concussion now by a simple shaking of my head as one would do to signify No. It will leave me with momentary confusion, dizziness, disorientation, a metallic taste in my mouth or other common concussion symptoms. I have had to learn to turn my head with my shoulders to slow the rotational speed so this does not happen.

The concept of once concussed, always concussed was discovered by research done back in the 1970's.