Anything recognizable is the property of the appropriate owners. I do not make any claim to ownership, nor do I make any money from this.
This is based off of the most recent BBC version starring Benedict Cumberbatch and Martin Freeman and J.J. Abrams' Star Trek.
Diagnosis
There are plenty of reasons it is said that the road to Hell is paved with good intentions. Otherwise, events spanning centuries might never have occurred. If Sherlock Holmes had known what would happen because he learned to have a heart, he might have lived alone. And if John Watson knew just what the future held, he might not have fought so hard to survive Afghanistan.
"John, that cough has lasted 13 days now, don't you think you should see a doctor?" Sherlock looked up from the laptop when his flatmate finally stopped hacking wetly into a handkerchief.
"I am a doctor."
"That doesn't mean you shouldn't see one."
"I'll see a doctor when you're actually considerate to normal people." The blond man sat back in his chair and tried to breathe deeply without triggering another attack.
Three hours later, John didn't miss the pointed way Sherlock kept his mouth shut while being ushered into another crime scene. Donovan stared suspiciously after the pair before going back to her duties. And then Anderson didn't know what to do when the detective suggested he stick his head in a loo with a 'please' tacked on the end. By the end of the rather short case, Holmes was physically biting his tongue to stop himself blurting out observations that might be offensive and John relented.
Of course John shouldn't have been surprised when Sarah was deemed too pedestrian and he was whisked half way across the city to a respiratory specialist only to be followed into the exam room by Sherlock. The one thing that kept him from sending the consulting detective back out to the waiting room was the concentrated effort the taller man was making to only ask questions regarding his health and left whatever dirty secrets he had deduced, as secrets. In the end, the specialist determined it was simply a nasty bout of pneumonia from a mid-winter plunge into the Thames and sent them on their way with a prescription for antibiotics.
"I told you it was nothing."
"Pneumonia is not nothing."
"You made it sound like I was on my deathbed."
"I can't have you being sick, it slows me down."
Recognizing that as being as close to sentimental as Sherlock got, the shorter man dropped the subject. A few days and he would be back to normal and the detective would return to announcing every little thing the people around them didn't want anyone to know. And he did feel much better after the antibiotics had run their course. Except there was still a slight crackling in the very bottom of his lungs if he exhaled too far.
If anyone should know that there are no secrets from Sherlock Holmes, it was the doctor. He had convinced himself he had hidden the uncomfortable sensation until he was abruptly woken from his nap by a cold stethoscope being pressed against his chest. John resigned himself to the fact that the detective would not just accept that it was the lingering effects of the pneumonia but he tried anyways.
"You still have fluid in your lungs."
Watson pulled his jumper down more forcefully than strictly necessary. "Everyone sounds like that after pneumonia."
"Not 5 weeks after finishing the antibiotics. You did finish them all, didn't you?"
He tried not to scoff at the hypocritical implication while reminding himself that the concern Sherlock was showing was a good thing. "Of course I took them all."
"We're going to get a second opinion." Sherlock announced and stood, the matter effectively closed.
The second doctor agreed with the first, and told Sherlock off for worrying over nothing. John then hurried his flatmate out of the office before the genius could tell the specialist exactly what he thought of his practice and his personal life. For the trip back to Baker Street, John was slightly concerned by how silent the detective was but at least he wasn't listening for every little crackle and wheeze that came out of the former soldier.
The next morning, however, found the doctor laying perfectly still as an MRI thumped and hummed around him. It was disconcerting being the center of Sherlock's attention for such an extended period of time, and he was sure there was nothing seriously wrong with his lungs. But that meant that the detective was pursuing this illness out of some reason other than evidence, which he never did. Finally, the voice over the intercom gave him permission to sit up.
It seemed to take forever for his flatmate and the new doctor to leave the little control room after studying the images. As every second ticked past, John alternated between being convinced they were all worrying over nothing and knowing that he was definitely ill. When the door finally opened, the grim look on the specialist's face was all the answer he needed.
Medical terms were thrown out and he knew the words, but the meanings weren't sinking in. Sherlock would have to repeat it all later once he had made a cup of tea and settled back in his chair in 221B Baker Street. Vaguely he wanted to thank the tall detective for taking control of the situation and convincing the doctor to perform the biopsy immediately. But he was completely terrified of what the results might show.
Every day for the next week, Sherlock was the first to fetch the post. He would carelessly toss aside bills and coupon flyers until the envelope from the third specialist came. The former soldier couldn't bring himself to demand the letter despite it being addressed to him and simply waited for his flatmate to tear it open. Nothing changed on Holmes' face as he read the results of the biopsy, but John's heart fell when the detective pulled out his phone and hurriedly punched buttons.
"I need a favor Mycroft."
John couldn't hear the older Holmes on the other end of the phone, but he knew him well enough to be sure he was lording over Sherlock's request.
"I need the best doctors you have."
He imagined that Mycroft was exasperatedly telling his little brother to simply visit St. Barts rather than bother him.
"It's for John."
Mycroft must have immediately agreed because Sherlock hung up his phone and picked up his coat. "I'm going to Barts. Don't wait up."
Watson nodded, eyes locked on the paper sitting innocently on the table. He couldn't bring himself to walk across the room to read the results. The doctor had known Sherlock long enough to know when he was fully focusing on a situation, and when he focused that intently, it was never a good thing. As the sun set over London, the flat steadily darkened but the former soldier was lost in a whirlwind of possible diagnoses, each more worrisome than the last.
Finally, long after the street lamps had come on, John pushed himself out of his chair and reached for the letter. Most of the words were unimportant to the doctor until he saw 'Cysts' and 'Test Positive' as well as 'Pleural Mesothelioma.' He had never seen a case of mesothelioma in all of his years as a doctor, but he remembered enough from training to know that it was serious and always fatal.
Sherlock eventually returned from St. Barts, arms full of files and books and set about researching everything he could find on John's diagnosis. Science had yet to find a cure, and even the very best care only extended the life expectancy a few years. John knew what was in store for him for the rest of his life and very briefly considered using his Browning as he had intended when he was first invalided back to London. But when he listened to his flatmate muttering about the idiocy of some doctors and their studies, he knew he could never do that to his friend.
John Watson was never one to back down in the face of adversity and decided that he was not going to be simply drug along by his diagnosis. He was going to fight for every day he could because Sherlock Holmes was fighting for him. Before he could settle himself in the chair across the table from his flatmate, the detective was holding out a file. For the first time in several days, the doctor smiled, glad that Sherlock was who he was.
The doctor fully expected Sherlock to tire of the subject as soon as Lestrade called with an interesting case, but when the DI bounded up the stairs, he was firmly denied without explanation. John simply shrugged and apologized. He wasn't quite ready to reveal his diagnosis to the Yard, though some excuse would have to be provided soon. From the medical reports he had read, it would quickly become apparent that he would be unable to keep up with Sherlock.
Once every bit of readily available information regarding his diagnosis and potential treatments had been absorbed, the duo prepared to tackle the larger problem of choosing a treatment with the help of Mycroft's specialists. Though, after only an hour of tests and evaluations, John was ready to murder the lot and say to Hell with his lungs until Sherlock's unmistakable voice echoed down the hallway.
"Don't you understand how important these cultures are? Take your incompetence and go!"
John took a deep breath and tolerated the poking and prodding for Sherlock's sake as much as his own. The detective would never admit that they had become dangerously co-dependent as soon as they had met. But the former soldier knew Sherlock would have trouble coping if anything happened to him before he was ready to let him go. What Watson didn't know was the extremes the consulting detective would go to in order to save him.