When he was shot in Afghanistan, among blood and sweat and adrenaline and pain was the knowledge that his time as an army doctor was ended, regardless of whether he survived his injury.
Civilians should not have bullet wounds in their shoulders or Brownings in their desk drawers; as a civilian, he could not succeed. But even before the helicopter arrived to bear him away, he knew that civilian life was imminent. Suddenly, the world of desert sands and comrades-in-arms was closed to him, and it felt like he was losing a greater part of himself than any projectile could ever displace.
Then, a certain consulting detective entered his life, and another world was opened. From surveying crime scenes to running about London, to listening as Sherlock predicted (with maddening facility) their fortunes when they went out for Chinese, to explaining (with paltry success) that shooting walls in bouts of ennui was A Bit Not Good, it was a world in which he immersed himself fully.
Sherlock Holmes became inextricably linked to John Watson, and John Watson was the same for Sherlock Holmes. To those close to the pair of them, it was no longer Sherlock or John; they were a conjunction—John-and-Sherlock, Holmes-and-Watson.
Perhaps that is why returning to Baker Street is so much worse than leaving Afghanistan, on the first day John Watson visits Sherlock Holmes inscribed in stone: He has lost more than a battlefield.
And it feels being shot.