After healing Sam Winchester, Castiel backed himself into the wall because he thought Sam was Lucifer. He just stared at Sam, and he wouldn't take his eyes off of him.
Dean Winchester kept his eyes on Castiel. "Uh, Sam," Dean said to his brother. "Why don't you take a hike?"
"But Cas is back," Sam said.
"Sam, do it now," Dean said forcefully still keeping his eye on his angel friend.
Sam lifted his hands in surrender, and he took a hike like his brother suggested.
"Dean, you can't let Lucifer escape," Castiel told Dean.
"Is that who you thought Sam was?" Dean asked in understanding.
"Sam?" Castiel asked in confusion.
Dean got up from his spot, and he took Castiel gently by the shoulders. "I'm going to remind of you this only once, Cas," Dean said. "You shifted Sam's nightmare to you. You do remember that, don't you?"
Castiel blinked in confusion. "Oh... oh, yes," Castiel replied. "So he's been seeing Lucifer?"
"Yes," Dean said. "I thought I told you that's who he's been seeing." He led Castiel to the bed.
"Have I apologized to you about all the things I've done?" Castiel asked him.
"Yes," Dean said. "You said shifting the wall is the only way you can show your forgiveness."
"Yes, yes," Castiel said. "I can live with that."
"Can you really, Cas?" Dean asked. "What if you hurt someone because you thought they're Lucifer?"
Meg leaned against the doorjamb. "I can help with that, Dean," she said. "The meat suit I'm wearing has degrees in psychology; I found out there's an opening. They're interested in me already."
"I guess it's a done deal, then, Dean," Castiel replied. "I don't need sleep the way you or your brother do."
Dean didn't like it, but he couldn't see anyway around it. He got up from the bed. "If there's any problems, Meg, call me," he said, walked to her, and gave her his card. He wrote his cell on the back.
"You know I will," she told him as she slipped the card into her back pocket of her jeans and as he walked down the hall to his brother.