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.