He's numb when his knees hit the floor.
Part of his brain is telling him the facts (John dead, bullet to the back of the throat, grey matter— pons, medulla, cerebrum, occipital, temporal and parietal lobes— blown out through occipital and parietal bones, weapon still in mouth, finger still on trigger, perfect crime scene) but the other part, the part that's louder and more conscious has gone entirely dead. His brain says don't contaminate evidence, but his hands slide the gun from between John's teeth anyway (chipped molars, bloody barrel, pieces of tongue), and his arms gather up the limp body (still warm, no heartbeat, oh god John is dead John is dead John dead John dead deaddeaddeaddead). The gore on the wall attracts his eyes, and his brain says catalogue it, but he doesn't, because John is not for gathering data. Someone yells "Bloody hell!" behind him, and there's a rush of action and questions, and it's just meaningless, stupid sound because none of them matter because John is dead.
There is a brilliant moment in which Sherlock's great brain thinks this must all be a mistake. Perhaps earlier, when he slipped the hallucinogen-laced sugar into John's coffee, he got some of the drug on his own fingers. Yes, that must be it; all of this is a product of his overwrought mind and very strong hallucinogens.
No. No, that can't be right. (hypothesis: wrong wrong wrong! extra precautions taken, hands washed, no oral/manual contact since then, traces on fingertips would be ineffectual anyway) Logic, in all of her bloody infallibility, says that, no, this is really happening. (John dead: empty flat, no blog, undisturbed sock index, who will buy milk?)
And then it dawns on him. (too slow, think faster, reach conclusions with more efficiency, sentiment makes deduction challenging)
John is dead because of him. Sherlock has, for all intensive purposes, killed John. (oh god oh god just wanted to test out the theory that was all that was all didn't mean to kill him)
Sherlock bolts to his feet, and the body hits the floor with eerie finality. His coat spins as he makes for the exit, and people leap to attention around him but don't converge. (like Moses through the Red Sea, John might say— would John really say that? can't confirm or deny, no frame of reference)
It's not like Sherlock to forget, but he finds later that he doesn't quite know how he exited Baskerville, only that he trembled and yelled and perhaps passed out, and the damned blood will never come out of his coat. The therapist Mycroft tries to hire sends Sherlock an email telling him that he experienced a breakdown, but he deletes her as well as the message. The following few days are equally blurry, but the detective is fairly certain the drugs are to blame.
Six days after John dies, Sherlock's laying sprawled all over the couch in 221B, confronting the ceiling. The cracked plaster (682 faults, nine water stains, six burns caused by chemical experimentation, one discoloration of unknown origin) is unresponsive, so he turns to look at the skull on the mantel.
"There is something wrong with you," it tells him.
He gives his best glare, gathers up his house robe with a histrionic jerk, and turns to bury himself in the sofa. The back of his brain buzzes, leaping from elephants to teacups to the roach that scurries across the opposite side of the room. Cocaine used to make his thoughts clearer, but now it almost stings, grabbing his strings of consciousness and trying them into one another, pulling, twisting, not thinking right. (thinking: case. case: murder. murder: John. John: everything leads back to John.)
When did he shoot up last? He's been losing track in the fuzzy aftershocks of the high, stumbling around in the convoluted insides of his head. (actual ramifications of human moving inside cranial cavity: violent. would result in blood-brain and destruction of pia matter)
He needs a case.
"Don't normal people have a cry?" It's John's voice.
Sherlock bolts to the edge of his seat with eyes peeled wide.
"Getting baked in the absence of the only person who will stop you is a bit not good, isn't it?" says the skull, speaking in John's voice. The morbid contours of its mouth are smiling.
There must be more cocaine in him than he anticipated; he hasn't hallucinated since his first and last affair with heroin. He frowns. "Piss off."
The skull doesn't go anywhere. "Don't you feel anything, Sherlock? Remorse? Shame? You must feel something. You killed the man."
Sherlock crosses the room in three hysterical strides, seizes the skull, and sends it hurling into the adjacent wall. Wire snaps. Something breaks. Bones (mandible, maxilla, frontal, sphenoid, ethmoid, nasal) scatter themselves all over the table, on John's open laptop (unfinished blog post: "And trust me, you don't want to be around him when he's bored. He's hyperactive, rude, arrogant"), across his papers (bills, lists, phone numbers of friends— friends, plural: John Watson had more than one friend), in his date shoes where they've been left on the floor (no girlfriend but maybe he was hoping— hope: useless).
Sherlock stands rooted in place and heaving. He gives a slight shiver.
"Sherlock, dear," calls a quavering voice, "are you alright?"
"Ms. Hudson, shut up!"
Sherlock does not understand why, despite the fact that he just screamed for silence, he is disappointed at its coming. He spends a moment waiting, fingers plucking restlessly at the strings of some invisible violin, but Mrs. Hudson does not ascend the stairs. Doesn't even leave her flat, in fact (television running, stove on, clink of teacups).
The silence is still for the slightest moment, then his brain is tearing itself apart. Get a case get a case get a case, it says, but another part is saying no, John would say to slow down, to stop, just stop it, Sherlock but Sherlock can't stop, he can't handle himself anymore, he doesn't even know what to do, and somehow the violin has found its way into his hands, and he's standing at the window, jaw set, neck taunt, frame trembling, bow poised.
A low, keening moan plays across the strings when he draws the bow over them, and he eases into it, eyes closing. Composition is taking place but at the same time it's not, because his mind is churning up new notes and then letting them fall away, not deleting them but simply allowing them to slip through the cracks. The violin murmurs its low dirge long into the wee hours of the morning, and when Mrs. Hudson finds Sherlock the next afternoon, he's collapsed into John's desk chair with the first sleep he's had in days.