The Yellow Wallpaper by Charlotte Perkins Gilman (1892)

The wallpaper is the first thing she hates: a smouldering, sickly yellow, its pattern sprawling and committing every artistic sin, stripped away in great patches where it has already been torn. She has been brought to this colonial house for the summer to rest, and rest is all she is allowed; her husband, a physician, has prescribed no writing, no work, no company, only the airy upstairs room with bars on the windows and a bed bolted to the floor. So she writes in secret, and what she records is the slow logic of a mind given nothing to do but watch a wall. Gilman knew this cure from the inside, and she renders it with terrible patience: the way the pattern begins to move, the way a woman appears behind it, creeping, shaking the bars by moonlight. By the end you can no longer tell whether you are watching a woman lose her mind or finally, fully claim it.