Upon reevaluating the passage, the emphasis is indeed on the narrator's acute senses, particularly the sense of hearing, and their assertion that being nervous does not imply madness. The narrator claims that they can calmly recount the story despite their nervousness.
While the passage initially suggests a juxtaposition between nervousness and madness, it also highlights the relationship between health (the narrator's claim about sharpened senses) and the idea of calmness in storytelling.
Given that, the strongest juxtaposition in the excerpt also may include:
being healthy and being calm
However, the primary tension conveyed is between the narrator's state of nervousness and their claim of sanity amidst that nervousness.
So, while both responses could be relevant, the primary focus of the passage warrants the conclusion that the author juxtaposes:
nervousness and madness.
Thank you for prompting the reassessment!