In "The Pit and the Pendulum," what does the narrator realize after his dream?

In this
story, the narrator quite simply realizes that his dream had not been a dream at all.  He tells
of how he swooned after receiving his death sentence from the Inquisition, and goes on to
discuss the process of awakening from a swoon:  In the return to life from the swoon there are
two stages; first, that of the sense of mental or spiritual; secondly, that of the sense of
physical, existence.

This is a discussion of his attempts to understand what
happened to him as he was semi-unconscious; he states that he can recall tall figures carrying
him down, seemingly forever.  And, as he notes above that one first notices ones mental or
emotional state as one is roused from a dream, the narrator first feels a vague horror at my
heart.  And only after this horror does he notice his physical environment €“ he is somewhere
dark, dank, and flat.  At this point he is absorbed by the mere consciousness of existence,
without thought €“ and then all at once his senses return to him, he is able to draw more
details from his surroundings, and in this state of full awakening the details of his dream fall
away.  As he says, Arousing from the most profound of slumbers, we break the gossamer web
of some dream. Yet in a second afterward€¦we remember not that we have
dreamed.

So, in the immediate shock of awakening in such a vile, ominous
environment, the narrator forgets everything he has experienced after the trial, only able to
remember it vaguely, after much intense mental labor.  And yet all this time he keeps his eyes
closed, afraid of what exists beyond his eyelids, afraid that everything he had dreamed and
everything he had felt was true.  And, unfortunately, in this fear he is
correct.