''I remember it happening, but after that, nothing. It's like it never existed," Maria Carrillo High junior Alex Wrenn said of the concussion he suffered last August.
Wrenn, a nose tackle for Maria Carrillo's varsity football team, was hit in the chin with the top of a football helmet during practice.
"I know what happened, I remember getting hit," he said. "But remembering it, I feel like it was something I watched. Not like it was me."
In the three weeks that followed, Wrenn had a hard time focusing in class and on assignments.
"I was missing homework assignments, forgetting to do them," he said. "And information I learned before was difficult to remember."
Robert Neid, a sports and family medicine physician at Kaiser Permanente Hospital in Santa Rosa, said such a side effect is not unusual.
"Common symptoms are a foggy head, where it's kind of hard to remember or focus (and) amnesia," he said.
Concussions, although not day-to-day occurrences on the field, are not unusual in intense, high-level sports.
"With any physical endeavor, there is risk," said Jay Higgins, who coaches the Maria Carrillo football team. "And it's our job to protect the kids. One way we do that is by getting the best equipment and making sure it's properly fitted."
Although high-quality equipment is better for preventing most injuries, there are some common misconceptions.