Sam woke up covered in cold sweat. His whole body felt flushed and achy. It felt like his muscles had just been through a triathlon with absolutely no training. He pushed off the covers, waves of heat coursing through him, making him feel nauseous and dizzy. As he struggled to expose his skin to fresh air, he somehow managed to get even more tangled. Panting, he rested for a moment, gathering his last reserves of strength to free himself from the cotton torture devices.
His eyes slowly adjusted and he remembered where he was. He was in the bunker somewhere, but it wasn't his bedroom, it was... It was...
"Mmmmmgh," something whined and he flipped around suddenly, making his head spin and his temples throb. There were shapes in the dark... Well, one shape on a bed, but how did that shape have three arms?
"Mmmmmmh," the thing whined again. It sure sounded a lot like Castiel, Sam finally realized. Well, it made sense. If he wasn't in his room, Dean probably had put him in some sort of infirmary, and Cas was infirm too. Nothing malevolent here.
Cas kept whining, crying and moaning, mewing so pitifully that Sam wondered if he was perhaps taking social cues from a kitten.
Then, he heard someone shhing him.
Dean?
What was Dean doing in here?
"Cas?" Sam heard his older brother whisper softly. "Shh. It's okay. It's okay. I'm here, baby, I got you."
It broke his heart to hear the sadness and desperation in Dean's tone. Cas kept crying, and Dean's voice broke.
"Please, Cas. It's okay. Just sleep. I got you, I promise."
His struggle with the bedclothes forgotten, Sam listened in disbelief as Dean began to sing quietly. He couldn't tell what it was that Dean was singing, but it was familiar and soothing. Sam felt a memory stir faintly, back from days on the road, when his father was gone, and he had nightmares, and Dean calmed him down...
A bittersweet realization washed over him. The days where Dean sang lullabies were long since over, which made him want to curl up and cry. But seeing that Dean had someone else to take care of, Castiel, no less, made him feel warm and happy for his brother. He drifted off to sleep as his rough, masculine older brother sang, saccharine and sincere, to his angel and, unknowingly, to Sam.
When he awoke the next morning (or afternoon, or evening), Dean was gone, and Sam wondered whether he was ever there in the first place.