Sherlock pulsating in front of John, blowing his way through the alleys of London; doing what he loved most; that was, of course, when it happened-
The jolt of pain.
John's ankle twisted, knee hit the floor and his breath caught. He bounced once, twice, on the cold gritted concrete, in dazzling pain but he barely registered it before he was once again moving as Sherlock was surely running, and he, determined, did not want to miss Sherlock in his prime (or get left on the floor) so he pushed down on his hands, put his good foot down and (deep breath) let his sprained foot follow (medical degree suddenly non-existent) to catch Sherlock-
Another storm of pain, watery blurs and time-lapsed images, as he fell. He bounced once this time, his landing being remarkably soft. John realised that he would be left here, until some poor person found him in the morning; Sherlock would have forgotten John (his second choice) to remember the game (til death do them part). With Sherlock, you either keep up or get left behind.
Opening his eyes, his vision filled with the unexpected.
"Sher-"
Hallucination indicated blood loss but he indulged, stretching out a shaking hand, ready for disappointment, towards that sharp jaw, imagining his fingers to resting on that unwanted frown, his thumb hushing those lips-
"John."
But expecting only air - not solid, touchable Sherlock.
John felt a jolt.
Not pain.