Sherlock was disappointed that John had not noticed earlier.
He knew that he had been making an effort to hide it, but not that much, and besides, John was a doctor.
He supposed that he wrote the mood swings off as a typical Sherlock thing, having seen some of his tempers at the best of times.
Pale and trembling occasionally? Well, John rarely saw him eat, so it was to be expected he wouldn't feel so great. Sherlock even suspected that John thought he may be anorexic. Because, as always, John sees but does not observe. The obvious lack of sleep for days when particularly focused on a case also seemed to help John explain away Sherlock's obvious fatigue.
The lack of sensitivity in his fingertips? John wrote it off as too much violin playing.
So Sherlock was a bit disappointed in John, and a bit concerned for himself, when he passed out on a chase. He worked up to it though, not just an unexpected 'why the hell am I on the ground and feel like crap' low. Nope, this one was much more impressive, starting with him falling, unable to run as his legs turned to jelly.
Sherlock had attempted to wave John on, fully intending to catch up in a minute, but he must have looked as dreadful as he felt, because John planted himself next to Sherlock, and despite all his insisting, called Lestrade instead of continuing the chase himself.
He claimed he was fine, just the result of not getting enough sleep or proper nutrition while working this case. He could tell John wasn't completely buying it though. Sherlock knew he must have been pale and sweaty, and he hoped John would wrongly deduce they were both resulting from the chase.
He sent John off to get orange juice ("Really John, I'm just thirsty. Some orange juice would work wonders."), and wondered how long he had, as his vision was blurring and he was finding it hard to concentrate.
Sherlock knew he should be more prepared, but hadn't had time to reload his pockets after yesterday's crime scene incident. If John had noticed then that he was ingesting a lot of what seemed like mints, he may have been suspicious, but instead was preoccupied by the double homicide, which Sherlock admitted was fascinating as soon as he was able to see straight and stand up.
Sherlock knew he would have enough time to test before John got back though (nearest Tesco's, likely running there and back, not all have the same layout though, getting through the queue assuming he does not go for the chip and pin machine). Yes. Plenty of time. So Sherlock stopped his pump temporarily before digging his kit out of his coat. (And John wonders why he wears the coat everywhere.) Although it seemed inevitable that John would find out today, Sherlock would prefer it be on his own terms, and not because John happened upon Sherlock's bleeding fingers.
But today fate had decided to screw with Sherlock, because he realized he might not make it until John came back, as his hands were almost shaking too violently to get the droplet of blood onto the tiny strip. But he managed to, along with getting blood in a bunch of other places (have to dry clean the coat, get Mycroft to do it) and waited impatiently, with failing vision, before he saw the result: 1.3.
And that was the last thing he saw before his vision faded to black, and he hoped John would hurry.
It's all just transport, he kept reminding himself. Which was why it was so awful that it kept betraying him.
Lestrade knew. Sherlock hadn't told him of course, but when you're watched closely for drug use, and one day collapse at a crime scene and have a seizure, people get suspicious.
He had convinced Lestrade, under threat of death and secret revealing, to not tell anyone else. This was before John of course, and when John did come along, Lestrade stupidly assumed that Sherlock had told him, or otherwise knew. Lestrade was betting on the latter, but was quite wrong. Sherlock had never lied to either of them, but John seemed to believe that not sharing the entire truth was equivalent to a lie.
But Sherlock was glad to have someone around who would know what to do when he collapsed, pale and sweating at a crime scene. Instead of assuming drugs, Lestrade would run to get him some tea with lots of sugar, or feed him a couple of biscuits.
Mycroft was entirely insufferable. Why he was the one to get the properly functioning pancreas, Sherlock could not explain. So he did the only thing he could- make fun of him for his weight. Sherlock had learned long ago that if he ate, and took a lower dose of insulin, that he could lose weight. Of course, it made him feel like crap, so he didn't do it anymore, preferring to have his brain functioning properly, but it seemed his body had grown used to staying this size, and even if he did eat, would barely change.
So if Sherlock ever saw the look on Mycroft's face that was indicative of him preparing to make a comment about needles or anything related to having a defective pancreas, Sherlock would cut him off, inquiring smugly about the diet.
Mycroft did care, obviously, which was why Sherlock had gotten the pump in the first place, waking up in the hospital after having a seizure at a crime scene (looked like a murder suicide, but it wasn't) to find that Mycroft had made all the arrangements and had left no room for arguments. Sherlock grudgingly obliged, knowing how useless it was to argue after Mycroft had made up his mind and had the full power of the British government behind him. And it wasn't entirely awful.
Mycroft not telling John, however, was much more interesting. Mycroft would never just blurt out the fact that his brother was diabetic, no, he wouldn't want to spoil it. He would have tried to get John to read Sherlock's medical files, but John would have refused. Sherlock was a bit disappointed that his brother hadn't tried harder or put in more of an effort, but what could he expect? Mycroft was actually respecting his privacy for the first time, and it was the only time Sherlock didn't want him to. Which explains a lot.
John... oh John was going to be disappointed with him when he woke up. Very disappointed. Because John is a doctor and he won't be able to comprehend the reasons Sherlock kept this from him. And Sherlock isn't entirely sure of the reasons either. But he knew that John would have wanted to know, but he hadn't told him. This was the bottom line.
And if there was one thing Sherlock hated more than idiots (well, perhaps not more, but they were both equally hated) it was disappointing John.
"I don't even want to hear it."
Sherlock was still a little fuzzy at this point, and blinked several times, as if clearing his eyes would suddenly make that statement clear to him.
John obviously recognized the disoriented look in his eyes and waved a hand at him.
"Never mind. We can talk about this later. Sleep," he ordered.
Sherlock really didn't want to obey, but it seemed his transport had other ideas. And it listened to John.
Before he even opened his eyes the next time, he could feel John looking at him. He opened his eyes, knowing that it would be a bad idea, bu he might as well get it over with.
"Right. So. I could tell you what an idiot you are, except you already know that. I could tell you that you could have died, but you already know that as well. I could even tell you that you should have told me months earlier, but you already know that too. So the only thing I'm going to tell you is how bloody terrified I was when I got back to you after picking up orange juice at Tesco's to find you unconscious in the alleyway. Bloody terrified!" He was almost screaming at this point, and Sherlock wanted to shy away from the loud words, but he couldn't. Suddenly exhausted, John collapsed into the chair next to Sherlock's bed.
"I figured out that you were diabetic, your meter was still sitting on your lap, flashing 1.3, and I called an ambulance. I couldn't wake you up to get you to drink any of the orange juice. I didn't know what else to do." John was whispering now, seeming close to tears. "It took the ambulance nine and a half minutes to get there. I tested you three more times. And every time, the number was lower." His voice was breaking now. "I will never be able to forget those numbers." Sherlock could barely hear him for how quiet he was whispering. "1.3, 1.1, 0.9, 0.8." John looked right at him and Sherlock could see his eyes almost, almost, glistening. "You had a seizure. I thought... I though you were going to die."
Sherlock hated seeing John like this, broken, vulnerable, afraid. It hurt Sherlock.
"Would... would you like a hug?" Sherlock offered.
Sherlock could see John consider this before accepting. It was a bit of an awkward hug, with Sherlock still sitting in the bed, and John reaching over the rail and avoiding tubes and wires. They stated like that for a little while, until John stood up, seemingly in control of himself again.
"We are going home, and you are showing me where you keep all your stuff. We are loading your pockets up and mine too. We are getting you a bracelet that you like and will wear. We are getting Glucagon, and so help me I will watch you eat and test every day if I need to. And," he added insistently, "if these conditions are not met, I will not hesitate to call Mycroft for assistance or tell everyone at Scotland Yard." He smirked at Sherlock, rather pleased with himself. Sherlock scowled, and grudgingly nodded.
Sherlock was secretly pleased with this turn of events, even though it meant John absolutely insisted on Sherlock eating something at least three times a day. John cared. And Sherlock cared enough about John to care about himself.
At least, that's how he explained it.