Jack and Jill went up a hill to fetch a pail of water. Jack fell down and broke his crown and Jill came tumbling after, Dean remembered that rhyme as he himself tumbled down the rocky hill. He and Sam had been running to lure a Wendigo from his hiding place when Dean had lost his footing and fell head over heels down the hill.
He could hear Sam calling his name above him on the top of the hill as he fell. Dean tried to reach out and grab something that would halt his sharp descent, but the effort was in vain. A moment later, he came to the end where it dropped off and Dean felt something strike his head hard before he lost his vision to black.
What seemed like hours later, he felt his entire world shaking. First thought was: oh crap, earthquake! The second thought was: what the Hell? There's no earthquakes here!
Dean opened his eyes to see Sam looming over him with wide, puppy-dog concerned eyes.
"You okay?" he demanded.
"Yeah?" Dean answered, more like a question rather than a statement.
"Yeah? C'mon," Sam pulled him to his feet, throwing one of Dean's arms over his shoulders.
Dean's vision tilted and spun every which way possible, but he remained upright somehow. Sam pulled him to the Impala which felt miles away and set him in the backseat.
"I wanna drive!" Dean protested.
"Nuhuh," Sam shook his head even though Dean couldn't see it and started the engine, "Not if you want to get us both killed."