What is the narrator from "The Pit and the Pendulum" dreading when the story begins?

At the very beginning of the story, the narrator is dreading his own execution.  He has been put on trial for unknown crimes during the Spanish Inquisition, and in the first few lines of the story we hear the pronouncement of his sentence – “the dread sentence of death.”  He has been condemned, and upon hearing the result of his trial, his senses leave him – he can see the judge, see the judge’s lips pronouncing our narrator’s fate, but sees them morphed into grotesque caricatures.  He can at first hear the words spoken at the trial in a murmur, as “the burr of a mill wheel,” but soon he ceases to process all sound.  And it seems that the “decree…[was] still issuing from those lips” long after the simple decision of death need have been pronounced.  We can assume that the judge is giving the details for the long bouts of torture the narrator would soon have to endure.

At this realization the narrator has a new dread – the prolongation of his fate – and begins to imagine “what sweet rest there must be in the grave.”  Soon after this thought sneaks into his mind he loses consciousness, only to awake to a nightmarish ordeal.