I <em>was</em> sick, sick unto death, with that long agony, and when they at length unbound me, and I was permitted to sit, I felt that my senses were leaving me. (1)
From the very beginning, we know that the narrator is in a sort of in-between state, moving back and forth between consciousness and unconsciousness, between life and the edge of death.
I had swooned; but still will not say that all of consciousness was lost. What of it there remained I will not attempt to define, or even to describe; yet all was not lost. In the deepest slumber – no! In delirium – no! In a swoon – no! In death – no! Even in the grave all was not lost. Else there is no immortality for man. (3)
Here, our narrator seems to argue for the persistence of some kind of consciousness, even at the point of death, although he's reluctant to define what exactly it is. Still, he argues that if consciousness didn't continue in death, there could be no immortality, no afterlife. At the very least, we know that our narrator, a heretic of some sort (why else would he be imprisoned by the Inquisition?), still believes in life after death.
Arousing from the most profound of slumbers, we break the gossamer web of some dream. Yet in a second afterwards (so frail may that web have been) we remember not that we have dreamed. 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. It seems probable that if, upon reaching the second stage, we could recall the impressions of the first, we should find these impressions eloquent in memories of the gulf beyond. And that gulf is, what? How at least shall we distinguish its shadows from those of the tomb? But if the impressions of what I have termed the first stage are not at will recalled, yet, after long interval, do they not come unbidden, while we marvel whence they come? He who has never swooned is not he who finds strange palaces and wildly familiar faces in coals that glow; is not he who beholds floating in mid-air the sad visions that the many may not view; is not he who ponders over the perfume of some novel flower; is not he whose brain grows bewildered with the meaning of some musical cadence which has never before arrested his attention. (3)
This is quite the philosophical musing from our narrator. It's a complicated and, as you can see, rather long thought, but you can break it down. Let's give it a shot! So, according to the narrator, when we awake from "the most profound of slumbers" (like, say, fainting and seeing hallucinations), we break a kind of dream barrier. What we mean is, whatever it is that we experienced in that "swoon" is separated by the thinnest of membranes. This awakening, though, has two stages. In the first, we return to mental and spiritual life; in the second, we recover our physical senses. In the narrator's opinion, in that first awakening, our minds are still filled with memories of the beyond, that swooning dream state. Unfortunately, it's hard to remember those things; it's difficult to even understand what separates us from that swooning state. For all we know, he says, that "gulf" could be just like the gulf of death.
All is not lost, though, for the narrator supposes that those memories from beyond, even if they can't be recalled at first, will come back eventually, and often without warning; and we are amazed when they do come. He then goes on to link these revelations with the creation of art and the work of the imagination. It seems, ultimately, that the narrator's harrowing experience has led him to understand how art and original ideas come to be.
So far I had not opened my eyes. I felt that I lay upon my back unbound. I reached out my hand, and it fell heavily upon something damp and hard. There I suffered it to remain for many minutes, while I strove to imagine where and what I could be. I longed, yet dared not, to employ my vision. I dreaded the first glance at objects around me. It was not that I feared to look upon things horrible, but that I grew aghast lest there should be <em>nothing</em> to see. At length, with a wild desperation at heart, I quickly unclosed my eyes. My worst thoughts, then, were confirmed. The blackness of eternal night encompassed me. (6)
For the narrator, the idea of being conscious of nothing is more frightening than encountering the most visible of horrors.
There was another interval of utter insensibility; it was brief, for upon again lapsing into life there had been no perceptible descent in the pendulum. But it might have been long – for I knew there were demons who took note of my swoon, and who could have arrested the vibration at pleasure. Upon my recovery, too, I felt very – oh! Inexpressibly – sick and weak, as if through long inanition. (24)
Losing consciousness is bad enough; it's worse when your tormentors are aware of your every lapse into insensibility – and are willing to take advantage of them.
As I put a portion of it within my lips there rushed to my mind a half-formed thought of joy – of hope. Yet what business had I with hope? It was, as I say, a half-formed thought – man has many such, which are never completed. I felt that it was of joy – of hope; but I felt also that it had perished in its formation. In vain I struggled to perfect – to regain it. Long suffering had nearly annihilated all my ordinary powers of mind. I was an imbecile – an idiot. (24)
By the end of his ordeal, our narrator can barely think. His mind works only in half-measures. He becomes an "idiot" in the way the term used to be used – a man mentally handicapped by fear.