It started after he left the grave, after he promised himself that he would keep going through his grief. There was that slight lean to one side and an almost insignificant slide in his hips that made one step more uneven than the last.
He stopped suddenly, staring at his feet and almost daring them to do it again, just to be sure. It was another minute before he took a deep breath and just kept walking.
He was fine, he kept reminding himself- he would have to be.
It was another week at least, before it got any worse.
He stumbled going up the stairs with arms held down by groceries (he'd almost bought too much this time, forgetting that he was-). He managed to steady himself before he crushed anything, but he still noticed the slight tilt of his hip, the phantom twinge in his leg, the tiny shift of his weight that made him miss the next step.
He ignored it.
That night he dreamed about the shot that had taken him out of the war- the memory of the pain and the terror the flames and the explosions and the screaming voices- they followed him even as he woke up with the memory of his dismissal ringing in his ears.
He'd been useful for a time, even with his limp and depression and the darkness that had followed him as soon as he had gotten off that plane- Sherlock had wanted him around and wanted his help- but now he was back to being the ex-army soldier with his stupid imaginary limp.
He was torn between leaving the flat and staying- on one hand, he didn't want to forget the memories that made the place home (the yellow spray paint still on the wall and pock-marked with bullet holes; the discoloured stain in the kitchen ceiling from one of his experiments; the skull that stared down at him every time his eyes wandered to the mantelpiece); yet on the other, it hurt to remember. A nostalgic chuckle would be followed by a sudden ache in his chest, the memory of loss and the millionth realization that Sherlock was really-
It was when he was organizing things a while later (not preparing to move, he told himself, just cleaning things up) that he found it again- the metal cane stored away in the back of his wardrobe, forgotten behind a winter jacket he hadn't gotten around to wearing yet.
He stared at it for the longest time, remembering the coldness of the metal and the tiny click it made when he walked with it, back when it had been the only constant companion he had since being discharged.
He pushed his coat back over it and didn't look at it again.
People started to notice. First Mrs. Hudson ("are you sure you're all right, dear?") and then Lestrade when they bumped into each other ("you sure you're leg's okay?"); Sarah at the clinic (although John brushed her off enough times that she stopped asking) and even Mycroft- although he merely observed and went on to apologize (again) for what he'd done (John still hadn't forgiven him).
It got harder to hide. The nightmares got worse (and not just the war this time- now there was a clear view of gray sky and a silhouette that fell). He stopped being able to sleep through the night, and the purple shadows under his eyes became all too common. He skipped work some days, too exhausted to get through a day trying to help people when he couldn't even help himself.
"You know, maybe," Harry suggested, when he finally gave in to her pestering, "you should see your therapist again."
There was a reason why John had avoided it. It would mean finally admitting that he was…dead, and not coming back. It was hard, harder than he'd imagined- it had taken him at least a week to be able to say Sherlock's name again, and weeks more to admit that there was no going back.
"You'll get better," Ella said, looking up from her notes ("not coping well with loss"). "I'm sure he would have wanted you to get on with your life."
John had looked away then and kept his responses short; he didn't want to hear what Sherlock would have wanted for him. No one knew Sherlock the way the people close to him had. To the rest of the world- even the woman John paid to listen to him- Sherlock Holmes was a fraud.
When he got home, he collapsed halfway to the sofa, his body no longer able to take the strain of trying to hide that he really wasn't okay.
He could vividly remember the last time this had happened, as he knelt on the floor by the coffee table; trying to force himself to breathe, torn between screwing his eyes shut to focus on calming himself down and keeping them open to avoid the images that flashed behind his eyes (the fall and the crowd and the blood and cold skin of Sherlock's wrist-)
He wondered then, as he curled his fingers into his knees (still breathing, still concentrating on getting up and moving on) how he had ever walked alone before he'd met Sherlock Holmes.