Sometimes the Doctor feels tired. He wishes he could take a day off, leave everything and just rest. But of course, there's way too much blood on his hands for him to be able to properly relax, as his last fellow Time Lord is never tired of reminding him. His last fellow Time Lord is rarely tired of anything, if it can hurt the Doctor.
Sometimes the Doctor catches himself on being actually jealous of the Master's seemingly endless energy, even if he usually does spend it on mocking him, trying to break the Tardis' security protocols or attempting to build a doomsday weapon out of a kitchen knife and an empty Jelly Babies' bag.
Sometimes the Doctor looks at the Tardis' door with longing and wants to go out, save somebody and run for his life, as he used to do so long ago. Then he notices the Master, looking at him with dark intensity, probably all too aware of the Doctor's thoughts, and the Doctor remembers the Paradox Machine and what exactly the other Time Lord is capable of doing even in the most primitive of times. The Master seems never to give up on his attempts to run away, rule some world or destroy another. If he escaped, it would be the Doctor's fault, so in the end they just never go to any inhabited planet. The Tardis changes into a prison for both of them.
Sometimes the Doctor allows himself to sleep and, on rare occasions when his dreams aren't full of nightmares and red grass burning, he once again wanders on another worlds. It's the only way out he has.
Sometimes the Doctor finds the Master sitting in a dark room deep in the Tardis, beating a rhythm of four against the table with one hand and covering his eyes with another, his whole posture speaking of exhaustion. The Doctor always comes closer and embraces the Master, if only to be pushed away. Sometimes, however, the Master simply leans against the Doctor, starts drumming against his back and after a long, silent moment falls into a shallow sleep in the Doctor's arms.
The Doctor may sometimes dream of things which aren't the Time War. The Master, even if fast asleep, never stops tapping with his fingers.