John gets home from the hospital (well, the pub, actually), and he's tired, and drunk, and probably coming down with a cold, which is why when he steps inside his apartment (and it really is his, not his and Sherlock's, not anymore) and he sees an odd shadow by the living room door, he doesn't become suspicious, doesn't go straight for the gun. No, that was the proper course of action when he was still living with the detective, and the doctor had learnt quickly enough that if he wanted to live a normal life - and not spend his nights in prison for attempted assault - he would have to give up carrying his gun wherever he went and answering the door with it for fear of thugs and evil masterminds and...
John remembers his first night in his new apartment and a knock after nightfall and moving like a thief in his own home, the gun safely in his hands. He had clicked off the safety and very carefully - very quickly - peered through the eye-hole, only to see one of his new neighbors standing there with a pie in her hands, smiling innocently (and he might have felt like an idiot afterwards, but the whole time he had spoken to the nice lady and thanked her for her thoughtfulness his left hand had been fingering the trigger on the other side of the half-opened door).
After almost three years of living a peaceful - boring - life, the doctor thinks his responses to danger and suspicious people and guns have dulled, once again become like that of a civilian, and he isn't sure whether that pleases him or not. In any case, his eyes pass over the strange shadow without stopping, and that is when things get a little strange - the shadow detaches itself from the darkness, and suddenly there is a dead man standing before him.
"Hello, John," the Sherlock look-alike says in a voice so much like the real Sherlock's that the doctor feels his breath hitch, even though he doesn't think he's ever heard the detective use those words before. It was always 'I've solved the case' or 'I need you to check on the human liver in the fridge' or 'Afghanistan or Iraq?' (or 'I want you to listen to me, John.')
The doctor scans the intruder's face furiously, desperately, trying to come up with proof that he is real even as John knows he is not (too much work and too little sleep and just a drop of alcohol seem like the reason for this hallucination, and he isn't sure if that makes him want to stop drinking and try living a healthier life or simply set up shop in one of the less crowded pubs and live the rest of his life in a drunken haze).
John's eyes pass over the tall figure so fast his stomach gets a little queasy, but he still can't figure out whether his hand would touch skin and curls and wool if he stretched it toward the detective or if it would simply pass through, and for a second or two the doctor wishes he was Sherlock, so that he would only have take one look at the other and know whether he really was there or if he had finally gone over the bend (and wasn't that a strange thought, seeing as it was Sherlock who was standing in front of him, looking a little ghost-like but more than a little material).
The doctor doesn't know how long he stays like that, simply analyzing Sherlock (because, real or not, it is Sherlock, no matter how much he wishes it weren't), but he is awoken from his stupor by the same thing that put him in it.
"John, I-" the tall man starts, a little awkwardly, and the doctor still doesn't know if the... thing in front of him is real or make-belief, but he's always had more common sense than most (unlike the detective), and he's seen Sherlock die and he knows the dead don't return from the grave (not even this one), so he pinches the bridge of his nose between two calloused fingers and he interrupts the hallucination before it has a chance to start again (and if his hands are trembling slightly, no one has to know) .
There is silence for a second or two. A silence not so much oppressive as it is assertive. The Sherlock look-alike appears to simply observe him for a moment of two, but John is sure his face does not betray him, mostly because it would be a little hard for it to reflect his feelings if not even he knows what they are.
"John, I don't think you understand -" the detective starts, only to be interrupted again.
"Oh, I understand, alright. And I want you gone." the shorter man cuts him off.
"But you need me here." the hallucination states, as if it is the most obvious thing in the world, and John thinks that, perhaps, to him, it is. Perhaps he - it - needs only to take a look at the cane in his right hand, the lack of any personal items hiding in plain view or the way the apartment looks decidedly untidy, as though whoever lived there couldn't be assed to clean up the place. When he thinks of it like that John admits that, yes, maybe it is that obvious that he needs Sherlock, needs his charm and intelligence and danger (though the existence of the first one is debatable). But, all the same, things are not the way they used to be, can never go back to it. He's come a long way from the day of the detective's funeral, changed in more or less visible ways, and some days he thinks that he doesn't want to go back to the way things were - the memories of his time with Sherlock have been thrown together with John's half-imagined childhood, his almost-idealized college years, and the stories about his great-uncle, Sean Watson, who'd once found a winning lottery ticket on the street, only to loose it again, along with his pants and what little common sense he still possessed in an unfortunate house fire. The nostalgia taints them all so much that the good doctor knows better than to take them at face value (he takes them not with a grain of salt, but with a whole mountain of it).
The point is that, despite all things pointing the contrary, John does not need Sherlock. Anymore, if he ever did. And, anyway, he knows - knows - the man is dead, just as he knows that this isn't really happening, and he has seen enough psychologists to know that it is better to nip insanity in the bud than to end up in a white padded room, with only your imaginary friend for company.
"That may be, but I still want you gone, need or not." John replies and turns his back on the figment of his imagination.
"Look, John, I know it's preposterous, illogical, irrational, whatever you want to call it, but I'm here, and I'm alive, and you'll have to deal with it sooner or later." The alcohol and exhaustion induced hallucination says this a tone that suggests it is starting to get annoyed. Funny, Lestrade had told him almost the same thing more than two years ago, only instead of 'alive' there was 'dead'.
John looks at the tall figure, takes in the pale, thin face, the hollow eyes, all the little things he swears have changed, and he opens his mouth to speak, closes it, clenches his jaw. In the end, he chooses to look away and head to bed rather than answer, but once he is in his bedroom, the door safely shut behind him, he doesn't feel so unaffected and in control anymore. He shrugs off his jacket (it appears that imaginary-Sherlock has as much talent at distracting him as the real one did) and takes off his shoes before collapsing on his bed, still in his work clothes.
The doctor feels tired and nauseated and simply disoriented by the night's events, and it takes him a while to sleep. Mostly, he cannot stop himself from playing his and Sherlock's conversation over and over again in his head, imagining all the things he could have said differently. He doesn't really regret his decision not to join the nuttier side of the world, but a part of him still wishes he had simply thrown common sense out the window and enjoyed the once in a lifetime opportunity to talk to the brilliant detective once more. Even if he is nothing more than a figment of his imagination. But what's done is done, John tells himself as he falls into fitful sleep, confident he'll probably never experience this hallucination again.
(And when he wakes up the next day to the smell of charred bacon and burnt toast and Sherlock's somewhat sheepish but most definitely real face hovering above him he doesn't quite know how to feel or what to do, so he socks the detective in the eye - twice -, before hugging the daylights out of him.
And John doesn't think he stops laughing with relief that day, but Sherlock doesn't seem to mind.)