They say that dreams come back to haunt you, and that sometimes that which you buried comes back to get you. But the Doctor didn't dream, and the past was the past, present and future to him, so it didn't bother him. That only left the mattter of being haunted...and haunted he was. By memories, by screams, by voices, by his own thoughts, sometimes.
Sometimes he was haunted by just two phrases: "What about you, Doctor? What are you turning into?" and "You would make a good Dalek." And he was haunted by the sight of the last Dalek - a survivor of the Time War, like him - killing itself because it couldn't stand what it was turning into: a half human hybrid with thoughts and emotions it couldn't handle. Right up to the last minute the Doctor had been shrieking for it's blood, willing to rip the creature apart with his bare hands if he could get hold of it.
And all the time, all the Dalek had wanted wad to feel the sunlight on its mutated, broken body, one last time.