But hey, it's just your brain.
And that's talking about being out a matter of minutes -- think about all of the movies you've seen where the character wakes up into some wacky misunderstanding hours later. In Pulp Fiction, the guy from the pawn shop has enough time to carry the characters to his basement one at a time, tie them to chairs and wait for his friend to arrive. By the time they wake up (not on their own -- they only wake up because their captor sprays water on them), Willis and Rhames can probably say goodbye to such helpful abilities as standing, walking, talking or maybe even waking up again.
And when you start talking about those TV show characters who are getting knocked out in every other episode, you're dealing with realism on the level of Elmer Fudd surviving getting flattened by a boulder. Concussions -- even mild ones -- have cumulative effects (as every football fan now knows). The more times you get knocked unconscious, the more severe your dizziness, disorientation and nausea will be each time. So, by the end of Back to the Future Part III, after being knocked out so many times in a period of like two weeks (or 125 years, depending on how you look at it), Marty McFly should be reduced to a drooling idiot incapable of walking by himself, let alone driving a DeLorean through time and space.
CRACKED: Ruining Back to the Future for you since 2006.