Gilman doesn't just tell us the narrator's mind snapped. She shows us a mind that found a final, horrible logic. When the narrator says 'I've got out at last... and I've pulled off most of the paper, so you can't put me back!' she's describing a psychological prison break. The wallpaper was the symbol of the 'pattern' of her life—the domestic imprisonment, the patronizing 'rest cure,' the dismissal of her thoughts. By tearing it down, she rejects that entire structure. But the tragedy is her freedom is only insanity; she's 'out' but crawling over her fainted husband. It's a victory that is also a devastating loss. The creeping woman she saw behind the pattern was always herself, fragmented and trapped. Merging with that figure means she's fully internalized her own oppression as her identity. It's less about a ghost and more about a psyche turning itself inside out to cope.
A lot of discussions focus on the feminism, which is central, but I always get stuck on the sensory horror. The ending works because Gilman makes you feel the texture of the madness—the smell of the wallpaper, the creeping, the gnawed bedstead. The 'hidden' meaning is in the physicality. Her liberation is a physical destruction of the room's decor, which to a 19th-century reader would be an ultimate act of domestic vandalism, a rending of the very fabric of the feminine sphere. She becomes the thing the room was designed to suppress: wild, unclean, uncontrolled. John fainting is the perfect final touch—the rational male authority literally collapsing before the 'irrational' female reality he created. The meaning isn't just in the words she says, but in the indelible image she leaves you with: a woman crawling, endlessly, over a man passed out on the floor. That image is the argument.