Final answer:
The question is inaccurately posed related to Montresor, as the given excerpts discuss different literary works and themes of mental health and moral dilemmas.
Step-by-step explanation:
The question appears to concern whether the character of Montresor in Edgar Allan Poe's "The Cask of Amontillado" has a plausible reason for feeling sick at heart. However, the question is posed incorrectly as none of the provided excerpts mention Montresor, and they appear to come from various literary works, including Herman Melville's "Bartleby, the Scrivener" and Charlotte Perkins Gilman's "The Yellow Wallpaper." These texts illustrate themes of mental health and moral dilemmas. With respect to Montresor, Poe's story is driven by themes of revenge and guilt which could contribute to Montresor feeling 'sick at heart' if he were to feel remorse for his actions against Fortunato.