The first time it happens, neither of them gives it much thought. It has happened to John before, so he is quick to forgive Sherlock's linguistic faux pas, and Sherlock even admits –in a vague, roundabout way- that his mind is linked to "the transport" and his age is catching up to it. They laugh the incident off and John kisses Sherlock on the nose before handing him the "thing you eat soup with". To be truthful, spoon is a rather silly word.
The second time it happens, it worries John because Sherlock strands himself on the way back home from the shop, and this turns a quick morning errand into a two-hour preoccupation fest for John. And of course the idiotic genius did not take his phone with him. But John cannot be mad at him when he finally returns, because Sherlock's eyes are soft and apologetic, and he did bring the milk.
The third and fourth time come together, and they startle John because they happen just as they wake up tangled under the sheets, wearing nothing, as is their habit.
"Who are you, and why are you naked in my bed?" Sherlock asks; standing as far away from the blond man as the wall will let him. "Is this my bed?" he adds in confusion. He covers everything below his navel with the sheet, snatched away and held as if it were a shield. John cannot say anything, but he doesn't have to. Slowly, the light returns to Sherlock's eyes and he loses his defensive stance. The rest of the day is spent in a blur of awkward apologies and silent attempts at making everything alright and normal again.
CT scans and MRI's are a great part of Sherlock and John's week. It is only necessary protocol; both the doctor and the genius know what's going on long before the specialist pronounces the name. Sherlock allows himself one single tear - John cries the rest of them for him-, which falls off his cheekbone much like fell off the hospital roof so many years ago.
Sherlock insists that nothing should change. He practically orders John to yell at him for not taking out the rubbish, as if they had never heard the terrible diagnosis and were still in the dark about why Sherlock sometimes stands in the middle of Baker Street, eyes faraway, hands hovering as they try to remember just what they were about to do.
When Vivaldi and Bach make way to traditional children's songs and then to basic musical scales, John gives away the precious violin. He ensures it goes to good hands, of course: Mrs Hudson's niece is a promising musician. Sherlock notices the empty space next to the couch, but he says nothing. He soon does not remember the warm colour of the wood or the smooth trembling of the strings, except sometimes as if in a distant dream.
The medicine is not helping. The Sudoku and crossword books John got to exercise Sherlock's mind are now but ashes, thrown into the fire in one of Sherlock's rage fits. John does not flinch anymore when they happen. He just locks up the good china and sits on the stairs outside their flat, where he can openly weep, knowing that the crashes and yells of the brilliant man losing himself inside will drown out his sobs.
Sherlock forgets how to tie his shoelaces, how to dress himself, how the telly works. He soon needs help to eat, which John provides with religious devotion. When that requirement extends to the bathroom, John simply learns how to manoeuvre Sherlock's long lean body onto and off the toilet seat. He kisses Sherlock quiet every time the retired detective tries to apologize or thank him.
Soon it becomes too dangerous for Sherlock to live in Baker Street, even with John looking after him. The senior facility –John refuses to call it a home, because home is back in their flat with the skull in the mantelpiece and the bullet holes in the wall- is packed with young, competent nurses who Sherlock deems acceptable. John visits so much, he is sometimes confused with a resident, except he walks with a purpose and does not have an air of abandon around him, unlike the other grey-haired men and women.
One day, Sherlock falls silent. John can see that it's not like Sherlock forgot words, because they're there, in his eyes. No, "the transport" has simply shut off the routes between the beautiful mind and the withered lips, which sometimes open and close with the likeness of an enraged fish. John knows what Sherlock needs, and takes to yelling at the nurses when they can't read the mind of their patient, who smiles smugly at John. He does not do so out of cruelty, but so little happens around here, a scandal is always well appreciated.
A memorial for Sherlock is held under the willow trees in the cemetery. There aren't many people there, apart from what John estimates to be half the homeless population who have not yet perished due to the winter; most of the others who would've been invited have long since passed away, as if to warn the afterlife that Sherlock was coming. John still mentions Lestrade and Mycroft and Mrs Hudson in Sherlock's eulogy; Sherlock would've never forgiven John if he forgot about the friends that made life tolerable for the detective. Angelo is there, white-haired and teary-eyed. Even Donovan and Anderson have the decency to look sad that the freak is no longer there. And maybe they are; Sherlock did cause contradictory feelings in almost everyone who knew him.
John ignores most of the pats on the shoulder and pseudo-comforting words that make up for the congregation's goodbyes. He stands at Sherlock's grave for the second time in his life, places a single forget-me-not in the built-in vase at the foot of the gravestone, wonders if the detective would've appreciated the irony, and reads the epitaph once again to make sure he remembers.
The next day, a change is made in the epitaph, but John does not have to worry about forgetting that. After all, it is his own name.