Jim had just decloaked the rocket launcher. The delicate bridge was going to tumble underneath his feet, with him possibly along for the ride. He had lots of rides before but this? Hell no. He hadn't been on a falling bridge since his youth--if Spock were here, he would poke in and say there are numerous instances where that did happen but that was relationship wise not literal--for a very long time. Jim was going to die.
Everyone, who he had known, was probably dead or dying.
He was from a era that had since been . . . written down in the record books.
Even if he did live then he would be treated as hero.
Also, wouldn't he age quickly?
Jim hadn't aged quickly once out of the nexus . . . yet.
Then he heard the screech of the metal belonging to the bridge conflicting against the rocks.
Jim did what he necessarily shouldn't do.
You know how you see your entire life flash through your eyes as your end is coming?
Pretty much why Jim froze.
Jim knew it was his end.
And then the bridge fell.
He just knew.
But maybe Jim was wrong then as he was half of the time.