Dean was calling for him, and Castiel could here so much need in his voice that his heart - or Jimmy's heart, as the case may be - skipped a beat before filling with terror that something had happened to Dean and he may not make it there in time.
The angel was partially mistaken. Dean was calling out for him, and there was need, but he wasn't in danger. In fact he was fast asleep, which Castiel realized as soon as he landed in the motel room, angel blade drawn.
Castiel quickly sheathed his blade, not wanting to scare either Winchester if they suddenly awoke. He quietly checked the bathroom room for danger, finding none. He returned to the main part of the motel room, taking up residence at the foot of Dean's bed, trying to determine what had brought him here.
He had to wait only seconds before he got his answer.
"Cas…" Dean moaned, turning on his side and wrapping his arms around one of his pillows. Castiel was taken aback. Dean was crying out for him in his sleep? Dean dreams about him?
Dean buried his face in his pillow, a content sigh spilling from his lips. His next two words answered Castiel's most pressing question: why?
"Love you."