LIFE DOES NOT = MOVIES

What we see in the movies:
It seems to happen in about a third of the action movies/TV shows ever made: Someone jumps our hero from behind, and the screen goes to black. Hours later, he wakes up in some strange place and has to think on his feet to make his escape.
We see it in Casino Royale, after Bond survives a car accident but before he gets smashed in the nuts over and over. It also happens in Pulp Fiction, when Bruce Willis and Ving Rhames are knocked out by the owner of the pawn shop and wake up bound and gagged, right before the guy decides to "bring out the gimp."

Quentin Tarantino has some issues.

When they wake up, the guys aren't happy about it, but they're otherwise immediately alert and aware -- Willis is even able to orchestrate a violent escape a minute later.
It also happens to Marty McFly at least once in every Back to the Future movie: He knocks himself unconscious and inevitably wakes up a while later in bed with his mother (or, in one case, a paternal grandmother who looks disturbingly like his mother).

But that's nothing compared to the repeated head trauma suffered by some TV characters -- you would see it happen repeatedly on Lost (usually with the butt of a gun) and Heroes (usually right before every commercial break). The character Giles from Buffy the Vampire Slayer was known for being a) super-smart and b) extremely prone to head injuries. These two things are not as compatible as you might think.
What would really happen:
We've all seen boxers and football players get knocked out for a few seconds and then jump up and continue playing the game (hell, it's happened to some of you reading this). But it's all about how long you are out. Experts say if you're ever out for more than five minutes, call a goddamned ambulance. There's a really, really good chance you have severe damage. A hit hard enough to keep you down that long means concussion or, worse, a traumatic brain injury or your brain may be goddamned bleeding on the inside.

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