Dean had wanted to spend his last year having fun. So, while he amused himself with a set of twins, Sam was researching a way to break Dean's deal with the crossroads demon.
He was all alone in the confines of his mind. All of the emotions that he felt were trapped in there with him. He desperately needed to find a loophole to keep Dean with him. Life would be nothing without Dean.
He read and re-read all the information he could find. He took notes and made copies of pages of books. It was all placed in a file that he studied over and over again. There had to be something that he was missing. Dean's time was running out and Sam hadn't found a clue as to where to begin to look for answers.
His research wound around in his head, trying to find a way to fit together to get the desired result. It didn't matter where he was or what he was doing, the activity in his brain was constant.
Sleep was just a dream. When Sam collapsed from exhaustion was the only time his mind gave him a break. Then, he'd wake up trapped in the same puzzle with pieces that didn't fit.
Sam's file doubled and tripled in size. His head pounded with everything he was trying to remember and fit together to resemble a plan.
Sam's last year was hell, tormented by the fact that he couldn't save his brother. In the same stroke, he failed to save himself. When Dean died, Sam went with.
Finally, Sam was freed from the walls of his mind. Even if he was in hell.