Question

why is the em dash used in the following excerpt from gilmans the yellow wallpaper? john is a physician, and perhaps—(i would not say it to a living soul, of course, but this is dead paper and a great relief to my mind)—perhaps that is one reason i do not get well faster. to indicate a change in thought to explain a concept to clarify the meaning of a word to introduce a list of items

Explanation:

The em - dashes enclose a parenthetical thought that is a digression from the main statement about John being a physician and its possible relation to the narrator not getting well faster. It shows a shift in the narrator's train of thought.

Answer:

to indicate a change in thought