Roderick Usher's illness was mental rather than physical. Based on the descriptions of suffering from nerves and fear given by Roderick himself, it can be deduced that he was experiencing acute anxiety.
Roderick Usher is one of the main characters of "The Fall of the House of Usher," a short story by Edgar Allan Poe. The narrator of the story is Roderick's friend, who was invited by the sick man to his house to keep him company. Roderick had a twin sister, Madeline, who was also sick with a mysterious illness, causing her to lose control of her limbs. The siblings succumb to death by the end of the story, and the narrator flees as the house also crumbles to the ground.