It's always the pressure that wakes him up. The rythmic patter-patter of water against his face. He thinks he can see dark eyes and dark hair standing on the top of the building with a coy smile as they jump off the edge into the rain below. He screams out, of course, 'don't do it!' or 'I couldn't stop him!' while in his head he knew it was the truth. He COULDN'T have stopped him.
L was already in too deep.
And even as they nod and smile sadly and turn away and Ryuk cackles as he forces a triumphant smile onto his face, something inside him is missing and suddenly things get boring again. And he sighs as he sets his keys down on the table and tells the Shinigami to go away so he can lie on the bed and think. His eyes close and his body relaxes and he tries to tell himself that its 'just one more person out of my way' but he's really thinking 'one more person gone to keep me going'.
Distantly he could swear he could hear something chuckling.
It's the middle of the night when he wakes after a dream and realises theres a crack in his ceiling, and water is dripping onto his face.