I believe that everything Brown saw/ heard was just his mind messing with him. I also think Brown may have died because in the story, last paragraph, last sentence it says,"... they carved no hopeful verse upon his tombstone; for his dying hour was gloom." I believe he died because of that quote. I think maybe everything was a dream as well because Brown may have been in a coma, while he was experiencing everything because if he saw an old man with a serpent cane that could have represented death, which may have meant that it was time for Brown to leave this world.