Hi. Did you forget to mention that this question is about "The Fall of the House of Usher"
Answer:
This reveals that the narrator thinks that his impressions about the house and its surroundings are not real, but are things created by his own head.
Step-by-step explanation:
The house and the whole environment around it triggers uncomfortable sensations in the narrator, he begins to feel bad feelings like fear, strangeness, discomfort, among others. He believes, that these feelings are influencing his impressions of the house. The impressions are good, but the narrator believes that they are all invested by his own head, that is, for him, the impressions he has about the house are fantasies, illusions, and unreal thoughts.