acknowledge the seriousness of his wife's mental and emotional state following the birth of their child. John subscribes to the "rest cure," which significantly diminishes his wife's mental health and exacerbates her postpartum depression and psychosi. John prohibits his wife from writing, socializing, and exercising and insists that she remain secluded in the upstairs bedroom against her will.

Refusing to listen to his wife and sympathize with her serious condition, John believes that she is suffering from nothing more than "temporary nervous depression" and a "slight hysterical tendency." He downplays her mental illness and is completely oblivious to the fact that she hallucinates by seeing images of caged women inside the yellow wallpaper on a nightly basis. At the end of the story, John's wife locks the door to the upstairs room, successfully tears most of the wallpaper off the walls, and creeps around the room like a woman possessed.

When he opens the door, John is horrified by his wife's behavior, perplexed by the entire situation, and overcome with emotion. John faints because he cannot stomach seeing his wife in such a startling condition and is shocked by her actions and appearance. John is also plagued with the guilt of exacerbating his wife's mental illness and realizes for the first time that he is responsible for her dramatic deterioration. His wife's shocking appearance and the myriad of complex emotions he experiences make John faint when he opens the upstairs door.

The narrator's husband (a doctor), John, has spent the majority of the story diminishing and even undermining the validity of the narrator's mental condition as a product of her imagination and weakness.  She tells us, "John laughs at me, of course, but one expects that in marriage."  A wife expects her husband to laugh at her?!  She is not a child being silly (although he does refer to her once as "little girl"); she is a grown woman experiencing a very real mental illness, not, as John tells all their friends and relatives, "a slight hysterical tendency."  We now understand that the narrator is likely suffering from postpartum depression, a condition that affects many women after the birth of a child.  It is not "slight," and it is not some little trifling illness that women imagine because they are hoping for a rest.  In fact, the narrator hates the rest that her husband forces her to take.  However, John tells her that "no one but [her]self can help [her] out of [her nervous weakness], and that [she] must use [her] will and self-control and not let any silly fancies run away with [her]."  In other words, her husband believes that the narrator's illness is the result of her overactive imagination, her "silly fancies," and a weakness resulting from her lack of "self-control." 

However, in the end, it is he who faints.  It is he who is too weak to face the truth of her condition and too weak to bear himself up under the weight of what his "treatment" has done to her.  The end of the story seems to point to the idea that it is not women who are mentally weak, though they might be (on average) the physically weaker sex; rather, it is men who are mentally weak for failing to realize that there is more to women's medicine than treating generic "hysteria" with rest, isolation, and imprisonment.  By having John faint, Gilman turns the tables on men like the narrator's husband, brother, and even Weir Mitchell, the doctor who John threatens the narrator with.  The narrator has found a way to feel empowered, though it required a complete dissociation with her identity. She now believes herself to be free because she is not trapped behind the wallpaper, but her husband cannot handle that truth she has created in her mind: he is the weak one.

John, the narrator's husband, is a product of his time; he has little understanding of his wife's mental state and how his actions are affecting it. At the end of the story, when she has essentially gone insane, he opens the door to her room and finds her "creeping" around the perimeter, where she has torn the yellow wallpaper away.

"For God's sake, what are you doing!"

I kept on creeping just the same, but I looked at him over my shoulder.

"I've got out at last," said I, "in spite of you and Jane. And I've pulled off most of the paper, so you can't put me back!"

Now why should that man have fainted? But he did, and right across my path by the wall, so that I had to creep over him every time!(Gilman, "The Yellow Wallpaper," library.csi.cuny.edu)

Naturally, John has no idea that the narrator believes a woman to be trapped behind the designs of the wallpaper, or that she has now placed herself into that role. His complete failure to understand her feelings, coupled with what appears to be a complete mental breakdown on her part, is too much for him to handle, and he faints. In this way, he shows that he cannot understand her emotional state, and he becomes a physical obstacle for her to "creep" over instead of a mental or emotional obstacle.

It's somewhat ironic that John, a doctor and man of science, should be the one to faint, when the narrator is supposed to be the one suffering from hysteria. Yet if we put ourselves in John's shoes for a moment, we can see that, under the circumstances, his reaction is entirely appropriate—for there is something undeniably terrifying about seeing one's wife creeping around the room to avoid suspicion for having freed an imaginary woman from the wallpaper.

As a doctor, John will undoubtedly have witnessed a lot of strange behavior among his patients. But he's never seen anything like this before, especially not in his wife, of all people. To see such horrible manifestations of mental instability in someone he cares about—although he has a deeply questionable way of showing it at times—is a truly shocking sight, one that even his robust nervous system cannot handle.

When John finally awakens from his fainting spell, he'll somehow have to deal with his wife's mental illness. He'll have to get used to seeing his wife in a terrible state for which he may not believe there to be a cure—and which he himself helped to cause. In short, he'll have to be strong, which means, among other things, not fainting at the sight of his wife's deranged behavior.

Throughout Charlotte Perkins Gilman "The Yellow Wallpaper" the reader comes to understand that much of the failure of the treatment of the unnamed narrator's "nervous condition" is due to the Victorian society in which she is held captive by the common law doctrine of femme covert [French for covered, (hidden) woman/wife].  Under this law the husband had virtually total control of his wife's life.  Thus, in every aspect of her marriage, the wife was repressed in this patriarchal society.  Added to this, was the prevailing wisdom of Dr. Weir Mitchell who contended that "post-partum depression" was a myth, and the real condition was only nerves.  For this condition, Mitchell believed in total rest without any mental of physical activity.  And, the narrator's husband John concurs completely with this diagnosis.

So, whenever the narrator pleas with him to allow her to go into the garden, or to have a window open, John refuses.  Compounding this problem, the narrator, made submissive by her repressed social condition, begins to criticize herself,

I get unreasonably angry with John sometimes.  I'm sure I never used to be so sensitive.  I think it is due to this nervous condition.

But John says if I feel so shall neglect proper self-control; so I take pains to control myself--before him, at least, and that makes me tired.

I don't like our room a bit.  I wanted one downstairs that opened on the piazza and had roses all over the window, and such pretty old-fashioned chintz hangings!  But John would not hear of it.

With her husband's domination, the deprivation of anything aesthetic and pleasing, as well as the loss of socialization, the narrator focuses upon "the hideous wallpaper.  Aesthetically repulsed by the lack of symmetry--"I never saw a worse paper in my life--and the "lurid orange and sickly sulphur tint" of its color, the narrator begins to obsess on this wall covering from which she can find no relief. Her concerns then turn inward and she feels that she is "a comparative burden already" to her husband.

Gradually, however, the narrator, a creative, intelligent woman whose talents are depreciated by her repressive husband and who is denied "stimulating people" whom she needs, focuses so intently upon the wallpaper that she imagines exerts "a vicious influence" upon her.  This, then, causes her to feel a sense of antagonism, "impertinence" in the paper with its "unblinking eyes" that are ubiquitous.  From this vision then emanates a "strange, provoking, formless sort of figure" that seeks to be freed from the horizontal bars of the yellow wallpaper.  The narrator initially fears this woman, who is really her emerging sense of self.  In her submissiveness, she wishes "John would take me away from here!"

When she voices her anxiety to her husband, he tells her not to think about it.  More and more she feels trapped until she must free this woman she is behind the bars of the paper.  However, instead of freeing her, the narrator's sense of self enters the wallpaper and is irrevocably trapped.  When her husband knocks, she ignores him, for she is no longer outside the insanity of the paper.  When he breaks down the door, John finds his wife crawling along the baseboard, mentally lost. As she creeps along the baseboard, he perceives her insanity for which he is responsible and faints.  Of course, she does not understand why, and simply continues "to creep over him every time!"