Complex sentence: The narrator has no memory of who he is and no understanding of what it means to be alive or undead, he has only the first letter of his name ("R") and a vague notion that something is not right with the world.
Split into simpler sentences: The narrator has no memory of who he is and no understanding of what it means to be alive or undead. He has only the first letter of his name ("R") and a vague notion that something is not right with the world.