At first you breathed just because that was what you remembered, it was a habit. Then you just … stopped. There was not conscious decision, you would wake up and realise that you weren't breathing anymore. Of course, you were still doing that out of habit – sleeping. You never really fell asleep, just lost consciousness, pretended that you were normal for a few seconds, because at first you were in denial.
Then it would hit you – quite literally, that you weren't normal anymore. The first time so hit your head, or pricked your finger or were punched, and you didn't feel. Then you realise that your numb. No pain. No pleasure. No heat. Everything looks black and white the older you get, it's you and the rest of the world. Then it's your kind and potential targets.
And it repulsed you, the first time you steal someone's blood. You want them to scream, to run, but they lie asleep. And then you taste it, the feeling sucked back in to your body for maybe ten seconds, and that's why you do it at first, for that little bit of feeling.
But eventually, it becomes a habit, and you're only doing it because that's what you've always known, you've lived in the dark so long, you've forgotten the light, you've forgotten how to breathe, you'd have even forgotten your name if it wasn't spoken to you now. The darkness is all you've ever known, and it's all you ever will know, for eternity. And that scares you down to the very core of your lifeless heart.