"The Pit and the Pendulum" exists on the razor-thin edge between life and death, consciousness and unconsciousness. Indeed, the narrator, when he's not trying to save himself, is more often than not "swooning" (fainting), coming in and out of consciousness, and losing and regaining his senses. And it's during these in-between states that his best thoughts are formed, and during which we get the best insights into his character. Why? Well, in these moments we have to question our own experience, to ponder what we think lies on the other side of life and in the depths of our unconscious minds. Heavy stuff.
In the end, we must think of the narrator's experience less as a horrible tale and more as a profound learning experience.
Even as Poe horrifies us – or perhaps because he does – he forces us to consider how such experiences would change our outlook on life and our notion of existence.