Sam was woken up by Dean's yelling. He jumped out of bed and quickly walked over to the chair by the window where Dean had fallen asleep, grabbing a knife from the table on the way. When he got there, he glanced around the room, looking for anything that could be responsible for Dean's outburst. Satisfied that there was nothing there, he looked at Dean himself.
His older brother was thrashing around, apparently in the grips of a nightmare. This was the first Sam had heard of anything like this; usually he was the one with the nightmare, while Dean slept through the night, quiet as a mouse. But here he was, yelling his head off.Sam would have to wake him up, or else the other tenants would complain about the noise. He shook him, but there was no response, other than Dean's continued yelling. Sam slapped him in the face, yelled back, and splashed him with water, all to no effect. What was he dreaming about that had him so wound up? Finally, after Sam shook him some more and called his name a few times, Dean bolted upright, causing Sam to jump back a few feet in surprise. Dean was breathing heavily, apparently terrified, and his cheeks were wet, as if he had been crying. He looked around the room, barely seeing Sam until he grabbed Dean's shoulders. "Dean, calm down, you're freaking me out."
Dean blinked blearily a few times, trying to figure out where he was. He looked at Sam, confused. "Sammy?" he said, incredulous. "But, you're dead…aren't you?"
Sam looked at him, not bothering to correct Dean on his name. Now was not the time. "Dean, you were having a nightmare. A pretty bad one, from the looks of things." Dean wiped his face with his hands, getting rid of the wetness. "So, you're not dead?"
"No Dean, I'm definitely not dead. What happened that would make you think so?"
Dean was still too much in shock from his dream to even attempt to hide behind his usual mask of confidence. "We were hunting for the hellhound, and I tried to draw it away from you, but it tore me up pretty bad and then went after you. It killed you, Sammy, I saw it. You were screaming, and there was blood everywhere and…" He stopped, looking at his hands as if he were expecting to see blood there. He shook his head. "It killed you. I killed you." He ended in a whisper.
"What do you mean, you killed me? I thought the hellhound did. Anyway, it probably wasn't even your fault."
"But I should have shot it earlier, when I was behind the tree. I had a clear shot, but I didn't take it. I killed you as surely as if I had shot you myself. I was supposed to protect you, and I didn't. I failed. It was my fault." He hung his head, shamed even though the event he was talking about had never even happened. Sure, they had been hunting a hellhound two ago, but Sam had shot the thing when it had Dean pinned. Sam winced inside, remembering what its claws had done to Dean's chest. He had had to sew the gashes shut after disinfecting them to make sure they didn't get infected; hellhounds were notorious for the wounds their claws inflicted, primarily because they ended up giving the victim a fever, during which the victim usually had horrible dreams about whatever they feared most. Sam had hoped that the fever would break overnight and Dean would be spared the dreams. Apparently it hadn't.
He felt Dean's forehead, attempting to determine if he still had a fever or not, but his hand got swatted away. Dean was obviously over the nightmare, or at least over it enough to go back to his usual self. "You tell anyone about this, and I'll kill you," he growled. Sam laughed; Dean was definitely back to his old self.