Sherlock had never believed in an afterlife. He knew for a fact that life was simply energy, a combination of cells and organs and blood and neurons – something that ended as soon as any of the aforementioned things stopped working. This knowledge was irrefutable and absolute; nothing anyone said would change his opinion, short of him actually dying and waking up in heaven (or hell, which was perfectly possible, should an afterlife exist). And, even if this occurred, he'd still be looking for inconsistencies that proved the spirit world he found himself in was simply a hallucination or a dream or something he was imagining because he was in a coma.
Now, however, Sherlock wished he wasn't as certain as he was.
Now, he'd held John in his arms as the man lay dying. He'd watched the light fade out of his eyes – a literary reference that Sherlock hadn't understood until that moment. And, when John released his last breath, Sherlock had watched the colour drain from the world.
And, as Sherlock's trembling fingers clutched at the bottle of pills, he prayed like hell to a god he didn't believe in that he'd been wrong all his life. Because, at the exact moment John's heart stopped beating, Sherlock knew that no matter how slim the chances of an afterlife was, he'd take it. If there was one chance in a billion, in a hundred thousand billion, that life continued once one's body was dead, then Sherlock would take that chance in both his hands and never let it go.
Because, honestly, even if there wasn't a life after death, Sherlock didn't think it would matter much. He didn't really want to live anyway.
