Sirius hadn't slept. It was a bit difficult, when he was too busy worrying his bloody ass off about where the hell his best friend was on the night he'd have to painfully and dangerously transform into a carnivorous beast. But, apparently, said best friend had found it unimportant to let him know where the hell he'd be. So Sirius spent the night and early dawn wandering about the city, searching for Remus everywhere he could think of and wishing he had his bloody map.
Finally, he'd dragged himself back to the flat-- just in case. And ended up collapsing onto the couch and falling into an uneasy sleep full of visions of Remus lying dead and mangled in the streets of Cardiff.
He awoke to the sound of the door opening and jumped up. He wasn't sure which overwhelmed him first or more intensely- the relief, or the anger. "Remus." The greeting- if it could even be called such- was low, and sounded more like Padfoot's growl than human speech.