The narrator is torn between the cultural norms of the day, which dictate that she is suffering from hysteria and needs to be isolated for her own good, and her ingrained feeling that she is simply depressed and requires an emotional and creative outlet. She knows that there is something really wrong with her, but cannot express it or solve it by herself.
You see he does not believe I am sick!
And what can one do?
If a physician of high standing, and one's own husband, assures friends and relatives that there is really nothing the matter with one but temporary nervous depression -- a slight hysterical tendency -- what is one to do?
(Gilman, "The Yellow Wallpaper," library.csi.cuny.edu)
Here the narrator's problem is seen; she asks the reader "what she can do" against her husband's accepted cultural diagnosis, but declares herself sick regardless. She thinks that she knows what she needs to get better, but cannot express that need to anyone, as it will be seen as a sign of her "hysteria." Instead, she tries to concentrate on the creation of a mental fantasy, which unfortunately becomes all-too real.
The narrator of "The Yellow Wallpaper" is in touch with the fact that she is slowly losing her mind. She admits that she is feeling better in "body," but her husband will not allow her to voice her opinion that she does not feel well mentally. Feeling isolated and not being allowed to socialize or have any "stimulation" of any kind only makes things worse for her. She knows that writing in her journal -- the means she has of expressing herself -- can be helpful for her condition, but she also has to sneak around in order to do so, and she finds this exhausting.