This could apply to Darren Shan when he first started drinking human blood after a friend got killed by the wolf man. After he did that, he retained the friend's memories, but he had had nightmares about it for a while afterward. He now knows that he can never go back to being a human and must remain a dhamphir until he becomes a full vampire, and then he will be that way until he dies and stays dead.
This could apply to Darren Shan when he first started drinking human blood after a friend got killed by the wolf man. After he did that, he retained the friend's memories, but he had had nightmares about it for a while afterward. He now knows that he can never go back to being a human and must remain a dhamphir until he becomes a full vampire, and then he will be that way until he dies and stays dead.