The third time Dean fell asleep in Castiel's lap was after they had escaped Purgatory. It was after Dean found out that Cas was alive, after they had rescued the prophets from Crowley, and after Kevin was safely tucked away with Garth.
Dean was worn out, and honestly, he was feeling pretty hateful toward Castiel. He had been shocked to learn that Cas had decided to stay in Purgatory of his own free will. It hurt Dean that his friend thought so low of himself that he believed he needed a punishment as bad as Purgatory.
Dean sighed, and ran a hand over his face. He glanced at Sam and found his brother sleeping peacefully on his bed. They had checked into some crappy motel room after saving Kevin. Cas was in his own separate room adjacent to theirs. Dean glanced at his watch. It was almost 1:00 a.m. He figured he should go to sleep. With a sigh, Dean shut his laptop, and climbed into bed.
After a year of sleeping on the hard ground in Purgatory, the soft mattress felt foreign and uncomfortable to Dean. It felt like he was sinking or drowning into the cushions. For the first few days after escaping Purgatory, Dean had slept on the floor. Then Sam started yelling at him about how Dean wasn't in Purgatory anymore, and that he should sleep on the bed like a normal person. Dean had sighed, and given in just to shut his brother up, but he regretted that decision.
The mattress creaked and bent under Dean, causing him to squirm in discomfort. He gazed at the hard surface of the floor longingly, but knew if Sam found him there asleep, Dean would have to listen to a whole lot of bitching and moaning in the morning.
After an hour of tossing and turning, Dean gave up on trying to sleep on the bed. He grabbed the blanket and settled down on the floor. He sighed in content as his back hit the hard, flat ground. Then he paused. Something was missing. Something that Dean hadn't had access to earlier, but it was here now.
"Cas?" Dean called softly, trying not to wake Sam. Cas appeared next to Dean instantly, looking confused.
"Dean?" Cas asked, "Why are you on the floor?" Dean sighed.
"I can't sleep on a bed anymore. It's too soft." Understanding flooded Castiel's face, and he nodded sympathetically.
"Why did you call for me?" Cas asked, and Dean started at the floor, his face turning crimson.
"I, uh...well, I thought that maybe you could stay with me? Just this one night, you know?" Dean asked timidly. Castiel's lips twitched.
"Of course, Dean. And it doesn't have to be just this night. If you want me to come again tomorrow, I would be happy to." Dean felt his face heating up, and he hoped that Cas couldn't see him that well in the dark.
"Okay, uh, thanks," Dean stammered. Cas smiled, and sat down next to Dean, resting his back against the wall and unfolding his legs out in front of him. Dean inched his way over to Cas, and placed his head in the angel's lap. Castiel's fingers methodically moved through Dean's hair in a soothing motion, and Dean felt himself being lulled to sleep.
Sam wasn't really sure what woke him, but around 3:30 a.m. his eyes flew open, and he stared up at the ceiling. He tossed and turned, trying to fall back asleep but to no avail. After a few minutes, Sam sighed, and got up to use the bathroom. He rubbed his eyes tiredly, and trudged over to the dingy motel restroom.
After a few minutes, Sam flushed the toilet, and sleepily started the walk back to his bed. He passed Dean's bed on the way to his own, and almost walked past it before doing a double take. It was empty. Sam groaned, knowing that Dean was probably sleeping on the floor. He turned around, expecting to find his brother curled up like a cat on the ground, but instead he saw something that made him jump out of his skin.
Castiel was calmly sitting on the floor of Sam's room, his back propped up against the wall, eyes open and staring at Sam. And Dean was in his lap. His brother, Dean, had his head in Castiel's lap. And Cas was stroking Dean's hair like they did this every day. Sam resisted the urge to slap himself to make sure he wasn't dreaming.
"You're not dreaming, Sam," Cas said as if he had read Sam's mind.
Sam blinked stupidly, and sat down on the edge of Dean's empty bed. He stared dumbfoundedly at his brother. Dean looked so peaceful sleeping in Cas's lap. It was a type of peace that Sam had never really seen in his brother. Dean's body was always wound up with tension, his shoulders tight, and his posture rigid, especially since Purgatory.
But now, Dean's body was relaxed, as if all the tension had somehow leaked out, and his expression was placid.
"Cas, what's going on?" Sam asked. "Why is Dean sleeping in your lap?"
"It's actually not that unusual," Cas stated. "It's happened a few times." Sam continued to stare at Cas like he had eight heads.
"What do you mean it's happened a few times?" Sam asked.
"In Purgatory. The ground was not really the best pillow, and I did not need sleep."
"Oh," Sam said faintly. "Well, if this helps him sleep, then I'm fine with it. Dean hasn't really been sleeping ever since he got back." Cas nodded.
"You can go back to bed, Sam. I'll look after your brother," Cas promised.
Sam nodded, and lay back down in his bed. As he drifted off to sleep, Sam decided that he was happy for Dean. He was glad his brother had finally found some peace.