what conclusion does the narrtor draw about usher's mental state

Usher is, like many Poe characters, suffering from some sort of mental malady which makes his senses hyperactive; thus he is hypersensitive to many things around him. The narrator sees Usher as somewhat of a hypochondriac, since illness runs in his family and he expects to be sick like his predecessors. He believes things to such an extent that he often carries them out - thus the burial of his sister.