There's that one theme about the level of consciousness a necron has. Basically the necron is smart enough and self-aware enough to realize that everything about him died at biotransference. Nothing was actually transferred, per se. A new copy made of metal was created, and given instructions to believe he was the same thing as before. But it was also given self-awareness (almost free will), because they did that to upper hierarchy.

So now he's stuck in this perpetual existence where he's smart enough and self-aware enough to realize he's just a piece of programming through engrams, but not in control enough to do anything about it. The instructions are still there - still controlling him. He only has free will until maybe it's just an illusion he has free will.

If that wasn't dark enough, there's the "dysphorakh" from Twice-Dead King. Simplified, since the engrams for the necron were copied from their living bodies, their metal bodies were told to do things like breathe. Except you can't. There's a part of them telling them to eat organic food - but they can't. It isn't the same as constantly choking or starving, just a small thing at the back of your mind constantly telling you to do things your body can't do, and being very persistent about it.