Twilight woke up, eyes sparkling in the sunlight flowing in through her window from another beautiful day! She stayed on her side as she stretched, taking care to keep her head over the side of the bed so that the constant stream of vomit would keep going into the drain she'd had installed under her bed. After all, her sheets were mostly clean. She kept them clean as she slipped out of bed, stepping into a quad of rubber boots she kept laid out just out of the splash-zone.
She walked over to her mirror, little booties splashing through the vomit that was pouring from her mouth onto the half-dried vomit she'd left on the floor the previous night. She kept her mouth open over the drain as she brushed her mane, the edges of her mouth turned up in a smile, as she noticed that she'd managed to go a second night without getting any vomit in her hair, which meant she didn't need to shower. Nopony showered anymore. Everything smelled like vomit anyway, so it's not like body-odor was a problem.
She walked out the door with a spring in her step, heading down stairs to the main room, where she would be meeting with her friends. This used to be their weekly breakfast day, but
Applejack had already sat down. Now that everypony vomited instead of eating, there was no point in farming apples, and it had really freeing up her schedule. She did plumbing now, more because she wanted to than needed to at this point, seeing as she had made enough money to retire several times over with all of the money she'd made installing vomit-drains when everypony realized that this was their lives now.
Pinkie Pie was also there, letting out gurgling giggles as she slid about on the floor. Sugarcube corner had been converted into a "waterpark", if by "water" you mean "vomit". Baked goods weren't really worth baking anymore, but vomit-slides had been all the rage ever since all the ponies had gotten over it.
Rainbow Dash flew in the window, a steady stream of vomit splattering beneath her. She did a backflip on the way to her seat, and the vomit flew in all directions, in a circular burst that would've been beautiful if it wasn't that sickly yellow-green color that this substance, which Twilight had yet to fully identify, for some reason had. The Wonderbolts had had difficulty doing their old tricks, now that vomit was a constant bodily function, but had adapted by incorporating it into their routines, selling Wonderbolt rain-coats and special "splash zone" tickets!
Fluttershy stepped quietly in through the door, even the sound of her endless stream of spew was gentle and graceful against the floor. She'd found the animals were much easier to keep now that she didn't need to feed them, and other ponies no longer minded the overpowering stench that came with entering her cottage.
Rarity walked in behind her, holding her head high as she showed off her latest outfit. All her clothing was made out of rubber, vinyl, and other water-proof materials now, and her "vomit chic" line had sold gangbusters, so she was also working just because she enjoyed it.
In fact, Twilight had realized, this vomit thing had been the best thing to ever happen to Equestria's economy: with ponies no longer needing to eat, breathe, or bathe (or use the bathroom, she'd realized after a few days), the cost of living was way down. To quote the title of the latest all-instrumental Hoofbeats single, All you need is puke! This had also been the great equalizer for the classes: no longer could the nobility turn up their noses at the commoners, because if they did, the puke would run back down their chins.
She closed her eyes and smiled, and would've sighed if she was still capable of doing so. She levitated her clipboard, writing on it...
"You know girls, I was worried at first, but I'm really starting to like this puke-based lifestyle!"
"Indeed!" Rarity replied, "Even Starlight and Trixie have managed to work out the complications in their little relationship! Did you hear that Trixie is doing vomit-based magic tricks now?"
"I know! We talked about it just the other day!" Twilight smiled, "She's so much more pleasant now that she can't talk!"
Spike, who was sitting in his own chair, gave her clipboard an odd look, crossing his arms. He didn't really care that his entire frontside was covered in vomit, nopony cared about it at this point, in fact, he'd been practically bathing in the stuff since it all began.
He took his clipboard and wrote something on it....
"Trixie can't talk?"
Twilight rolled her eyes, "Well, she can, but obviously she has to write it down, because she can't stop vomiting. Nopony can, obviously."
Spike stared at her, his vomit running in a river down the side of the table...
And that's when Spike did something which shocked every pony in the room...
He stopped vomiting...
...And spoke.
"Wait..." he said, the first words they'd heard outside of a phonograph in over a month, "You mean you actually can't stop?"
Twilight reached out with her magic, grabbing her marker and frantically moving to keep writing on the board.
"WHAT? NO!" she scribbled down, "HOW DID YOU STOP?"
Spike shrugged, "Dragons never had to vomit, Twilight. We all just figured that was just the new thing and chose to go with it."
Twilight's eyes were practically bulging out of her head, scribbling more down, "IF YOU DON'T HAVE TO VOMIT, WHY ARE YOU VOMITING?"
He stared at her incredulously, completely baffled that it wasn't obvious, and stated an answer for the ages...
"Dragons like to vomit."
He opened his mouth, and promptly went back to vomiting like everyone else.