why is Raskolnikov suffering in part 6?

Rodion spends hours wandering about in a mental fog. He seeks solitude, but no matter where he is, Rodya feels someone else's presence. "The more solitary the place was, the stronger was his awareness as of someone's near and disquieting presence, not frightening so much as somehow extremely vexing." We have already noted that he seems to possess two selves, and it is possible that this other presence is, in fact, that of his other self.