The Dragon Doctors brings us the story of Rina, who was Taken for Granite and left for two thousand years in a cave with nobody to talk to and no sensation at all (thankfully, she was only conscious for the first days). Fortunately the eponymous doctors rescued her. The comic also features Tanica, who was accidentally turned into a tree by Sarin. She can communicate with the others through magic, though.
Sarin actually was turned into a tree by his/her mentor as a lesson.
It's later revealed that a government did this to people who broke their no bodily alterations rule, just in case those people were ever needed. How useful those people would be after years, decades, even centuries as statues is questionable at best.
At one point some criminals petrified the crew of a Coast Guard ship and threw them overboard. Not only were they still conscious they could feel the water flooding their lungs so it was like drowning without end.
xkcd did a pretty literal one; it also skewers a classic schoolyard Lame Comeback as well.
In Drowtales, Kharla'ggen of the V'loz'ress clan has a creepy hobby when it comes to dealing with those who catch her fancy or resist. She uses her vast demonic powers to twist and turn their flesh, changing them into living breathing dolls and proceeds to use them to play dress up and snuggle.
In the completed sprite comic In Wily's Defense, Dr. Gabriel Knight was killed in a lab accident, but his soul survived in one of his incomplete robots through some divine intervention. The robot was kept frozen in stasis, unable to move or speak, but Gabriel could still see and hear everything happening in front of him. His wife, also a scientist specializing in robotics, disappeared for a year to mourn. Needless to say, Gabriel had completely lost his marbles by the time the robot was finished.
Florence in Freefall has had (mercifully brief) periods like this, thanks to her programming. In one instance, she's ordered to be happy; she complies outwardly but confesses to screaming on the inside. In a clearer instance, she has her voluntary movement suspended for an upgrade without warning; as soon as she gets it back, she shrieks belatedly.
In Girl Genius, there is a plant that gives off a pheromone (or something) that induces feelings of extreme happiness, and then eats the prey (similar to a Venus Flytrap). Apparently, this plant takes over a year to fully absorb large (read: human-sized) prey. So far, Tarvek and Zola have neglected to mention exactly how quickly death comes for a victim.
A manga link. It's from the artist who did the Idle Minds.
Not quite over, for those of you who thought you'd escape sane. (The pictures to go with the first strip's ending narration.)
Ian Samson is a big fan of illustrating "turned into an object" comics. He's done things like having the super-heroine Synthia Stretch trapped forever as a bouncy ball toy. A girl with clay-based shapeshifting powers losing her ability to control her form and being turned permanently into a clay urn. And possibly most disturbing, a girl who's witch sister has ruined her life by constantly turning her into various articles of clothing. The witch eventually assumes that because she has no friends and no social life, she must prefer being an object, and decides to stop turning her back into a human. Unable to complain, seeing as how clothes don't have vocal cords, her sister spends the rest of her life trapped as one article of clothing after another.
Being one of his works, City of Reality deals with a lot of this. Magic World is full of people who, thanks to Hinto Ama, have been transformed into all manner of things, from turtles to clothing to water. At least there's the Manumitor, who goes around saving as many of these victims as he can.
In fact, in this work, the trope seems slightly subverted as usually the author's works seem to heavily imply that a person will be stuck forever. In City of Reality, it is mostly heavily implied everything will be okay eventually.
Jack by David Hopkins has a short story about a guy who gets offered a very nice apartment for free, ostensibly so he can convince other prospective buyers. The apartment at first seems to be everything promised, but strange things start to happen. He hears strange moaning sounds in the neighboring apartment, and his girlfriend tells him that he can't leave. After inadvertently killing her, a duplicate shows up and tells him nothing in the apartment is real, and that his girlfriend has long since forgotten him and moved to other guys. He takes a sledgehammer and breaks down the wall to find the strange moaning, and finds some sort of strange muck monster that limply chases after him, and he barely escapes through the hole in the wall, which closes itself. The person who sold him the apartment shows up and demands to know what's going. He is told that the truth is just out the front door, but he won't like it, and there is no going back to the nice apartment he once had. He ignores this and opens the door anyway. He is instantly reduced to a pathetic thing that he saw in the other apartment, too weak to even stand up. The apartment interior turns into plain wood similar to a shack, with nothing but a chair for him to sit on, and the only sound he can make is the moaning he heard earlier. It turns out he's in a particularly unpleasant part of Hell. And he stays there.
In Namesake, Selva, the Wicked Witch of the East, turned the Munchkin King into a hat box and Selva herself is turned into a purse
While Jane's fate is played for laughs and she might not even mind her new existence so much in the end (it's not really evident), a version happens to another much more sympathetic character without any especially magical or scifistic means: Kept alive indefinitely by advanced medical technology but too hurt to be healed or for the pain to even stop, suffering from the same extreme agony permanently whenever conscious. It makes the "must scream" part literal.
This sort of thing happens way too much in The Wotch. Scott has been transformed into an immobile, conscious statue three times so far, though it didn't last very long. Rosetta wasn't so lucky, as she got turned into a statue by a crazy wizard, kept that way for some time, then released after said wizard's Heel-Face Turn—but then she was turned back into a statue by a basilisk without anyone knowing what happened to her. It's been mentioned that some statues in museums and mannequins in department stores are transformed people. And some people consider this a humorous comic.
This also almost happened to a demon early in the comic's run...before the Big Bad and The Dragon rescued him.
In The Zombie Hunters, the Basilisk zombie possesses an automatically paralysingbioluminescent gaze. Any human that locks eyes with a Basilisk will suffer a painful seizure and become immobilized. The victim then has no choice but to lie there helplessly as the zombie closes the distance to feed. Slowly. Starting with the face.
Start of Darkness, one of the prequels to The Order of the Stick, initially plays this straight, when Xykon traps the soul of Lirian the druid in a magic gem, raises her corpse as a zombie, and threatens to feed the zombie to an ogre, thinking that it will drive her insane. Later subverted when he traps the soul of her lover Dorukan in the same gem. Because Evil Cannot Comprehend Good, he accidently creates a You Are Worth Hell situation instead.
Sarda from 8-Bit Theaterwent back to the beginning of the universe, and is forced to live through every major event in the universe over a period of BILLIONS of years. He admitted that the only thing keeping him alive at that point was pure, unadulterated hatred of the LightWarriors.
Chaos' plan was to put everyone into this type of state.
"I'll use my supergod powers to lock the souls of all livings things on this plane in the eternal torment of the darkness between worlds."
The Helmsman from Homestuck. Formerly the Ψiioniic, ancestor of Sollux and follower of The Signless, he was captured by Her Imperial Condescension when the Signless' rebellion failed. She extended his lifespan indefinitely with her magic, lashed him to her spaceship, and used him as a living battery to massively overclock her ships power. He exists in a state of undying, perpetual agony for thousands of years before he is killed by The Vast Glub.
In Verlore Geleentheid, Jane Onoda was in cryogenic stasis for 10,000 years but, due to a computer glitch, she and the others on her ship were conscious the whole time. The only reason she stayed (somewhat) sane is that the ship's computer kept her occupied with battle scenarios against the species that nuked her homeworld.
"It grows from here. Reginald begins reducing more and more actions to simple lines of dialogue: "nod", "dance", "laugh", "love". Eventually his muscles atrophy; his body wastes away. Only the left hemisphere of his brain remains alive, the spoken word itself reduced to mere thought. And once Beartato earns his master's degree and invents a brain-to-speech synthesizer, that final thought is at last heard: "Weep a single tear for the life I have wasted."
Schlock Mercenary had an AI disconnected from the mainframe, but still left running, with no sensor input and no way to control anything or alert anybody to her predicament. AIs in that universe operate so fast that they don't experience time the same way as humans do; a few seconds of real time is like millennia for them. This AI is left in this state for several hours, which seem like endless eons to her, while everyone else is unaware of her situation. By the time she is finally reconnected, she has gone murderously insane.
MS Paint Masterpieces: Played for laughs for a few strips in the second game adaption when Reset Man's AI is placed in a storage device.
The backstory to at least one character in morphE. Between days there are dream sequences that reveal piece-by-piece how the seedlings came to be inside crates. One character in the second sequence was depicted as hanging by their wrists against a wall, too weak to do much more than kick off the wall and hit their back on the rocks behind. Their narration explained that their stomach was all but eating itself from hunger and their throat was too dry for them to speak beyond a husky whisper. The only candidates for this trauma both spent over 4 months between their kidnapping and escape. Hanging. Alone. Unable to die.
The Adventures of Sue and Kathryn! gives us the Haunted Tree, which keeps telling Kathryn (to her frustration, as she's asking the tree for its opinion on other matters) to "release me from this existence".
Slightly Damned has Hell, a place of eternal personalized torment. It isn't that bad when you consider you could also end up in the Ring of the Slightly Damned, an almost entirely empty wasteland of nothing but rocks and mountains. And the only three known occupants have left the Ring, one dead and the other two in the world of the living.