Burning, searing pain across his chest. But worse then that, it was inside too, as Death's hand pushed it into place. It was electrical, shooting through his body, every nerve on fire. He felt it melding with his body, felt it click into place an, even as he screamed in agony and protest, he knew there was nothing he could do. Goddamn them! Couldn't they let him live without a soul?
His arms, legs, every part of his body was straining against the restraints, but to little effect. He wanted to bolt, wanted to push Death away, wanted to rip out the soul and throw it away. It was torn and useless, why would he EVER want it back?
It fit perfectly. Of course it did, it was his wasn't it? Death removed his hand, and the pain stopped. But far worse then momentary pain was the... the tingling the soul made. It tingled, itching, and he remembered Death warning him not to scratch at it, or else the wall put there would come falling down, but how could he ignore it?
Then the soul took over again. It wired into his brain, his body, and tapped into his consciousness, and the old Sam came rushing back in a hurry. But as it surfaced, the body it was in, Sam's body, had passed out. That was okay. It was a soul. It would be there certainly when he woke up again.
Okay, so this is my first story which has no Castiel in it. Do not expect this often. I just wanted to establish that I believe the old Sam will be like he was before the devil's incident, until the wall breaks down, which it undoubtedly will, judging by how the characters in Supernatural are tormented.