(HealthDay News) -- A jarring and forceful blow to the head can result in a brain injury called a concussion.

The American Academy of Family Physicians lists the following warning signs of concussion, which should be evaluated as soon as possible by a doctor:

* Headache.
* Difficulty seeing.
* Dizziness.
* Difficulty concentrating, memory loss or confusion.
* Problems retaining balance.
* Nausea.
* Ringing in the ears.

One in every 12 American teens (about 2.1 million) ages 12 to 17 experienced major depression in the past year, according to a report released Tuesday by the Substance Abuse and Mental Health Services Administration.

There was a large gender difference, with 12.7 percent of females and 4.6 percent of males reporting major depression. It's defined as a period of two weeks or longer of depressed mood or loss of interest or pleasure, and at least four other symptoms -- such as problems with sleep, energy, concentration and self-image -- reflecting a change in functioning.