Final answer:
Roderick Usher suffers from a mysterious illness described as a family evil with symptoms that include acute sensitivity to stimuli. His condition mirrors the decay of the Usher family and their ancestral home, illustrating a deeper metaphorical sickness. Edgar Allan Poe uses this parallel to intensify the story's dark and fatalistic theme.
Step-by-step explanation:
The illness Roderick Usher suffers from in Edgar Allan Poe’s story is not explicitly named but is described as a “family evil” with symptoms of a “nervous affection.” Roderick displays hyperesthesia, or over-sensitivity to stimuli like light and sound, which is part of his acute bodily illness and mental disorder.
The connection between Roderick’s psychological state and the physical environment is heightened through Poe’s use of mirror reflections to emphasize the theme of a shared doom and the crumbling family line, as well as to intensify the dark and fatalistic mood of the story.