Answer:
"By long suffering my nerves had been unstrung, until I trembled at the sound of my own voice."
Step-by-step explanation:
This is the line that best conveys the insanity of the speaker. In this sentence, we learn that the character's "nerves" had been "unstrung." This is another way to say that the character was under such stress he had lost his sanity. He emphasizes this by telling us that he was so upset he trembled at the sound of his own voice.