Frustration at his father, anger at himself, relief that Dean is alive in the back seat.
Headlights, a moment of fear-darkness.
Awareness comes quickly, memories flooding his mind, pain overwhelming his senses. He tries to reconcile what just happened-tries to actually remember where he is (You're in the Impala-open your eyes, you're in danger).
Eyes open, blood running down his face, arm screaming in pain-movement at the back of the wrecked car-there is the danger.
Thoughts start to go together cohesively. Where is the Colt? He reaches into his jacket, feels the cool metal, pulls it out and props it in his lap, facing the oncoming threat. The door is ripped off it's hinges-a normal man with abnormal black eyes, there to finish what the semi did not. Sam's adrenalin surges as he defends his family. His threat is real, he will use this precious bullet on this worthless demon. The demon senses the young hunter's desperation, decides to vacate the human sack he stole-live to kill another day.
Relief washes over Sam as the abandoned truck driver becomes aware of his surroundings. Sam couldn't care less about this man-his father, his brother, are not responding to his calls, his pleas. He hears the trucker calling for assistance, trying to assure the occupants of the wrecked car that help is on the way, trying to apologizes for what he apparently did to them. Sam barely hears him, unaware of his own pain now as he struggles to get out of the car-to reach his unnervingly still brother.
No movement, no sound, so unnatural for his usually hyper older brother. Sam reaches out an unsteady hand to feel for a pulse. There it is, faint, but there. A sigh of relief-oh thank god-a unrestrained sob-legs give out from under him as he falls to the ground. Suddenly, shock as he sees the Colt still in his hands. He hears the sirens in the distance-the Calvary is coming, and the gun is vulnerable. Another adrenaline surge gets him to his feet. He stumbles to the trunk, still latched, but crumpled just enough for the gun to be shoved through. The protections he drew are still in place-even in death the Impala will protect the Winchesters and their most valuable weapon.
Job done, Sam falls heavily to his knees. He crawls to the gapping wound that was once the driver's side door, needing to be the guardian to his brother, his father. The pain he had managed to push away comes back in full force now. Cracked ribs push against battered lungs, head throbbing in time with each heartbeat, damaged wrist shooting pain up his arm. He tries to keep it at bay, but the darkness claims him, stealing the youngest Winchester from the pain of his injuries, the responsibility to protect, and the fear of loosing all that he loves.