Syntax refers to sentence structure and word order. Any deviation from a typical sentence structure can give us clues about the speaker's state of mind.
Twice in these sentences, the first and the fifth, the speaker interjects, inserting a related idea within the idea she was already describing using em dashes (—). This could indicate her level of distraction, that she has so much going on in her head at one time that multiple ideas or thoughts try to force their way out at once. Her many turns of phrase also mirror the wallpaper's abnormal pattern.
In the third sentence you ask about, rather than list the items in the series the way we typically do, with one conjunction before the last item only, this narrator includes the conjunction "or" before all items but the first one. This is called polysyndeton, and here, it has the effect of compounding the ideas involved. Again, we get the sense that there is just so much happening inside the narrator's head and her ideas gain momentum and snowball.
In addition, throughout the passage you cite, the narrator employs a number of dependent and descriptive clauses, complicating her expression of ideas. Her many clauses and vocabulary possibly indicate how nuanced and complex her ideas actually are. She is clearly quite intelligent.