"Sometimes it doesn't change anything," he affirms. Or nothing significant enough to be noticeable, or perhaps something that only manifests under very specific conditions. (How would you know you were immortal until you were supposed to die but didn't, for example?)

At her question, he makes a face. "I'm always conscious, asleep or awake. In the months I've been here, I've been unconscious... six times." She can probably see why that would be maddening. Technically it shouldn't even be possible -- the brain needs rest, it needs to be unconscious to store short-term memory into long-term memory and heal and all kinds of things. But he's been changed to be able to function this way.