I didn't see it myself. [It had happened just before he was given the Turk pin, when he had been drifting and barely living, not able to deal with what had happened after the labyrinth.] But Reno saw, over the network someone asked Jason to remove their collar, they died immediately, crumpling up like the pressure here was too much for them.

They did have puncture wounds around their neck, though as far as I could tell when I was in my dead world I wore no collar and my neck had no marks.

But it is difficult to tell truth from illusion here.