There is a scene in Philip K. Dick's Eye in the Sky where a woman enters her kitchen but discovers that her cat has been turned inside out, making him into little more than a mass of pink flesh blindly creeping around the kitchen... and it is still alive and conscious.
The scene in Do Androids Dream of Electric Sheep where Isidore attempts to repair the artificial cat which isn't artificial!
The Three Stigmata Of Palmer Eldritch actually scared PK Dick himself. In the early 60s, Dick had a hallucination of a supreme evil God with a metal face (a vision inspired at least partly by childhood memories of his father's stories about World War One and his gas mask). The Three Stigmata was Dick's attempt to exorcise that vision. As he wrote in 1979:
Some reviewers found it a profound novel. I only find it frightening. I was unable to proofread the galleys because the novel frightened me so.
The whole premise of Colony which makes you were up against a certain other shape-shifting extra-terrestrial monstrosity instead. Imagine an alien on board that could replicate anything as long as it was inorganic. Basically, anything on board, something as simple as putting on a pair of gloves can get you killed. Not to mention at the end, when they try to escape by boarding another ship in the nude, except they board the wrong ship.
Furthermore, if you really want to take this whole concept into Nightmare Fuel Territory, the creature they dealt with here isn't a whole lot different from The Thing (outside of the fact that one can only imitate life forms and the other can only copy non-living things). Now imagine the two of them being together. That's right, you'd have to be paranoid of everyone and everything.
What The Dead Men Say: In short, a super-powerful businessman dies of old age but his body is frozen and hooked up to a machine designed to allow him to be temporarily revived at various intervals- just enough to hear his thoughts. The whole idea of "half-life" is a bit eerie in itself but imagine that no matter where you were on Earth or even outer space you couldn't escape from him. Every time you turn on the television you just get a picture of a distorted face and hear faint, feeble mumbling; every time you pick up the phone, you hear the same mumbling, along with... well... any other human creation (the story makes references to this taking over newspapers, telegraphs, and an "electric typewriter"- so basically a computer) that could conceivably be used to communicate information.
"The Gun" has an intriguing premise involving a group of space explorers finding ancient alien artifacts, something complicated by the fact that the aliens in question built a giant cannon programmed to shoot down anything that flew over their airspace (including the protagonists' spaceship). The heroes manage to disable the gun and make off with a large pile of ancient artifacts which they intend to present to Earth. Unknown to them, automated machines are repairing the gun and this time arming it with nuclear warheads, meaning that something very bad might happen to the next group of explorers to come.
The protagonist of Silvia Everywhere (also known as Upon The Dull Earth) makes an arrangement with his girlfriend's not-so-imaginary-friends after she dies to bring her back to life - but it turns out they aren't quite sure what they're doing (humanity's original demiurge has long since moved on to even higher spiritual planes), and he quickly discovers that every human body everywhere is becoming a living Silvia as she was just as she died, in what must be next to Gyo on the scale of the most bizarre zombie apocalypses ever imagined. He is able to outrun the spreading transformation for a while, but finally he succumbs as well, and the last lines of the story describe his own thoughts as they are replaced with hers - lost, alone, oblivious, and very, very confused about what has happened.
The way Sylvia is resurrected is pretty creepy to begin with, and sort of foreshadows the ending: The "angels" (as Silvia called them) can't bring her old body back to life or create a new one from whole cloth, so they have her take the place of her unknowing, unwilling sister Betty - transforming her body and mind into Sylvia's when neither know what's going on. Betty isn't a very sympathetic character, but what happens to her is pretty traumatic.
The Hanging Stranger is one of his stories where the Paranoia Fuel is at it's most blatant: The main character, Ed Loyce, sees a corpse hanging from a street light one night. Everyone he points it out to treats this as an Unusually Uninteresting Sight, rationalizing that the body is supposed to be there because otherwise the proper authorities must have done something by now. He then uncovers an alien invasion plot, realizing everyone around him was brainwashed by aliens, and he leaves town hoping he can get this to the authorities before it spreads further. It already has spread further, and it turns out he fell right into their trap: The hanged body was deliberately left in public so that the aliens, disguising themselves as authority figures, would quickly be able to notice anyone who they didn't brainwash yet. They had used the body of another non-brainwashed man that they had caught with the same method, and at the end of the story Ed becomes bait himself.