Time Lords didn't need as much sleep as humans, but The Doctor was finding it more difficult to find things to occupy his time than usual while Rose slept.
He couldn't quite believe that she was here again. Nine was having a hard time controlling all the emotions having her so near was awakening. He wandered the hallways of the TARDIS, allowing himself to be comforted by the familiar sounds of his ship's machinery, the whirr of the console, the soft crying of Rose...
Wait.
Taking off down a corridor, he followed the noise to Rose's darkened room.