Sherlock had no idea why, but the very idea of losing any of his friends was the single most terrifying thing to him. Not just John, though he was obviously primary in these concerns, but also Mrs. Hudson, Molly, Lestrade, and even Mycroft to a degree. Not that he would ever tell his older brother that sometimes he noticed the care given and appreciated it, that was not how their relationship functioned.

It was frustrating not to know something, doubly so when it was about his own psyche. He had seen that others did not feel so frightened about the prospect of losing loved ones - frightened, yes, but not as much as Sherlock. Why? He would normally attribute this to the death of a friend in the past, or even a friendship gone sour extremely significantly, a traumatic experience from which behaviours such as these grew. But there were none. He had never possessed a friend before John Watson.

Which was why when the shot came, Sherlock was already out of the chair and straining against the cuffs as far as they could go, wrists protesting the pain. Moriarty's voice filtered through to him and he forced himself to sit, relax again, though his eyes were harder than before.

"I'm hurt, Jimmy, I thought this was a game between you and me, why involve John at all?"