Sherlock woke up.

If he was right, which he usually was, today he would be Sherlock Holmes, best man.
Yesterday he was Sherlock Holmes, consulting detective. Not that he wasn't a consulting detective today, because he was, but he was more than that, because he had John.

He stretched into his body and padded out to the kitchen, where John would not be waiting for him, because John would be at home with his wife.
His wife.
Sherlock smiled, and helped himself to the tea Mrs Hudson had kindly left. It was only lukewarm, but he'd finished an experiment involving the microwave recently, so he decided against using it.
Unless that was the other one.
(It wasn't, he realized after a quick peek through the door. It really definitely wasn't.)

So he drank his room temperature tea and planned what he would do for the day or so before he fell asleep and woke up in the other one.

He'd check and see if Lestrade had any cases (Sometimes there was crossover between the two, and he could use things from the one to solve the case in the other. Save time, and was safer.) then stop by and visit the Watsons. Mary was nearing her due date, and Sherlock wanted to spend more time with them before a baby was thrown in the mix.
(Not that he didn't look forward to the baby, because Sherlock was thrilled, even if he never told anyone that.)

Maybe he'd talk them into going out for dinner, maybe they'd get takeaway, maybe they would play cluedo and Sherlock would actually win for once. Perhaps he could take his violin and play to Mary's swelling stomach, to sooth the kicking baby held inside. Perhaps he could show them how well his scar was healing, to reassure Mary yet again that he had forgiven her.
(Because he really had. He understood, and he knew, and he forgave her, always and completely.)

He finished his tea, and examined his smile in the mirror.
(He didn't want to frighten the baby when it arrived, and he'd been informed that his smile could be... overwhelming.)
Shortly after, he shrugged into his coat and scarf and hailed a cab, violin in hand, just in case.

Sherlock woke up.
Today he would simply be Sherlock Holmes. Maybe he would solve a crime, perhaps he and John would go for a chase, maybe out to dinner after it was over, but that would be it.

(And then he would sleep, so he could wake up in the other one, the one with Mary, where John smiled and his wife was expecting, and Sherlock could feel his heart leap with happiness every time he saw both of them looking so joyous.)

He mulled over the previous night, a lazy evening filled with takeaway and laughter at the Watson house.
He missed it already.

But he stretched into his body and padded out to the kitchen, where John would be waiting for him, tea and a sarcastic quip at the ready.

Maybe even a nice murder.

Sherlock woke up.

He stretched into his body and winced as he pulled the wrong way on the scar tissue that was still new and pink and delicate.

He examined it in the mirror. Scars were interesting things. He had quite a collection, some he was fond of, others he'd erase in a heartbeat if he could, but the scar from the gunshot wound and resulting surgery was by far the most interesting. As was the story behind it.

Getting shot was messy, because he kept flipping back and forth as he woke up, during surgery, from anaesthesia, in the ambulance when John called to him. It was disorientating and hellish and he wasn't sure what was up or down or real or not.
The doctors were probably concerned because he was sleeping too much, but he hadn't entirely figured out how the whole transition thing worked, even though he'd been trying. (He always seemed to leave the notes behind, no matter which way he was going.)
But despite all that, he didn't wish to leave that one behind. He didn't wish to turn his back to Mary and John and the unborn child, simply because of a stray bullet.
Perhaps not exactly stray.
Well, definitely not stray.
But Mary was forgiven. Always. Completely.

He wouldn't give them up for anything. So he put up with those days (weeks) of confusion, bouncing back and forth, not really staying fixed in one place.

In the one he wasn't shot, he was stupidly tired, which concerned John, and led to him actually insisting on blood tests, which Sherlock allowed because he knew he couldn't reassure his friend any other way.
What was he supposed to say, that he'd been shot by his wife in his other reality? That the exhaustion was probably due to blood loss and the recovery and did he mention he was shot?
The tests were normal, and John just concluded it was exhaustion from working too much.
Sherlock let him think that.

But he recovered and healed and eventually he was nearly back to normal, and John could rest easy with Sherlock back on cases and chasing after murderers and blackmailers. (Or about as easy as he could rest, given the circumstances.)

Mycroft was a constant. Sherlock didn't know how, or understand, since they never spoke about it, not using any words at least, but it was sort of mutually recognized that was just the way it was.
(Sometimes he wondered if Mycroft was everywhere, in more than the two places that Sherlock had. If he had two, who was to say that everyone didn't have more than one? What if someone had three, or five, or thirty? Was Mycroft a constant in them all? Probably, Sherlock figured. Mycroft was like that.)

Ever since he'd come back, from those two years when he'd been dead and gone and away, there had been two. Two lives, two universes, two separate realities. He'd fall asleep in one and wake up in the other, but that didn't mean he was sleeping in the other while he was awake in the one. (It was messy and random and never consistent, and he hated that.)

At first he thought John, or maybe Mycroft, or someone else (hell, all of them even) was playing a cruel joke on him, when he woke up one morning and John was living in 221b again.
Sherlock stared blankly at him, but didn't mention anything until he brought up the topic of John's marriage, and John gaped, bits of toast falling out of his mouth.

Because apparently in that one, John never met Mary, and was not to be wed.

Sherlock didn't understand it.

It didn't help the next day when he awoke and John wasn't there. A quick text proved John to be at the flat he shared with Mary.

Sherlock stared at his phone, wondering if he was losing his mind.

After a week of the same thing occurring, he came to a few conclusions. One, sleeping caused the flip. Two, the main difference was Mary, but that wasn't the only one. Three, his body didn't completely shut down in the other one, or time was different or something, because it wasn't simply on and off like that. Time wasn't linearly split between the two. Four, he was possibly insane, or would be headed there, simply because he was living like this. Five, he couldn't tell which one was real.
(And as a bonus point, before he realized what was going on, before the incident with the train, he'd flipped back and forth several times without realizing it. God only knows what he said that made no sense when he thought he was somewhere he wasn't.)

He wondered if the one with Mary was the correct one, because it was the one he saw first when he came back, but that didn't mean anything. He'd fallen asleep after Mycroft's extraction, and woken up, so which one was that? Had he been flipping back and forth ever since he'd stepped off that roof? Had he been flipping his whole life, and just not realizing it because they were nearly identical without Mary's appearance?

God, it made his brain hurt.
He hated not knowing.

So Sherlock just went to bed and hope that it would stop.

Sherlock woke up.

He didn't get out of bed and stretch into his skin, free of surgical scars. Instead he just lay in bed and mulled over a number of things that he'd only thought about hundreds of times before.

He didn't want to be there. He didn't want to be in the one where John was sad over his morning tea for reasons he couldn't understand. He didn't want to be in the one where Mycroft stuck to his diet. He didn't want to be in the one where he stole the letters from Magnussen's office and didn't get shot and everything was fine. He didn't want to be in that one.
He wanted to be with happy John and Mary who was due any day now. He wanted to poke fun at Mycroft and examine his healing scar and ask Molly how her cat was and share tea with Mrs Hudson and look sad when no one could see him.

How was he supposed to tell what was real?

Was anything real?

Maybe both of them were. Or neither.
Or maybe just one. Was it a test? Was he supposed to be figuring out which one was the real one?

God, this was hard.

John had gone on another date, because he was not married. Sherlock slipped into his room and pulled out the gun from its hiding place, and went back to his room.

He sat on his bed, looking around his room (which was exactly the same in both), eyes landing on the periodic table. In the other one they'd discovered a new element, 117.
(Was that supposed to be a hint? Could it exist? Was he supposed to discard the other one on the basis of scientific impossibility?)

He sighed, and examined John's gun.
It certainly felt real. Everything felt real though. That was the problem. He'd been over the problem again and again, researching philosophy and physics and psychology. None of them could explain it.

But they couldn't both be real. It didn't make sense.
And to Sherlock, that was the hardest thing. He wanted the world to make sense, needed it to.
Desperately.

So Sherlock closed his eyes and thought about what made him happy.
John. John made him happy. John being happy was the best thing in the world.
Mary. Sherlock loved Mary, in the same way he loved John.
Their baby. Even though it wasn't born yet, Sherlock loved that baby.
Solving cases. He could do that in either one.
But three of those things, three out of four of the things that made him happy, could only be found in one place.

And he wasn't there.
He was here, with a quietly sad John who didn't know what he was missing, with cases that seemed hollow, with unblemished skin, with no memories of a stag night or attempted murder at a wedding or the happy surprise that Mary was expecting.

If here was real...
If that was the real world, then he didn't want to live it in anymore.
So he crossed his fingers that this wasn't the end, and placed the gun to his temple.
With a deep breath, he pulled the trigger.

Sherlock woke up.