Two books you must read, if you have not done so already.
The Yellow Wallpaper
by Charlotte Perkins Gilman, 1892.
This disturbing short story chronicles the descent into madness of a woman who has been virtually imprisoned in the upper floors of a summer retreat home. Forbidden to do anything but lie in bed, our increasingly unhinged narrator becomes obsessed with the wallpaper in her room:
"It is the strangest yellow, that wall-paper! It makes me think of all the yellow things I ever saw — not beautiful ones like buttercups, but old foul, bad yellow things. But there is something else about that paper — the smell! ... The only thing I can think of that it is like is the color of the paper! A yellow smell."
The King In Yellow
by Robert W. Chambers, 1895
Most likely inspired by Charlotte Perkins Gilman's story of three years prior, The King In Yellow is one of the most influential - and most overlooked - works of Gothic horror ever written. A collection of short stories ranging from sci-fi fantasy to romance, The King In Yellow's first four tales - The Repairer of Reputations, The Mask, In the Court of the Dragon and The Yellow Sign center around a fictional play entitled The King In Yellow, which drives insane anyone who dares read it. The play itself does not exist, and Chambers offers only eerie excerpts to tantalize his readers.
Having read the collection entire many times over, I can safely say that it won't drive you to insanity...but I must admit: I felt considerably "altered" after having read it.
The King In Yellow would go on to influence many modern writers of horror, most notably H.P. Lovecraft, who refers to the play in several of his short stories. The King In Yellow itself was inspired by both Poe's "The Masque of the Red Death" and the Ambrose Bierce short story "An Inhabitant of Carcosa."
Camilla: You, sir, should unmask.
Cassilda: Indeed, it's time. We have all laid aside disguise but you.
Stranger: I wear no mask.
Camilla: (Terrified, aside to Cassilda.) No mask? No mask!