Turns out the Reaper simply and silently turned and left the classroom; a few minutes later, someone ran into the room looking for him, as he was part of a schoolwide program on drunk driving (but of course this hadn't been announced to many of the students at my university, and certainly not to me and my class).
I had a severe stress reaction later, starting at lunch, when I began shaking, and the incident activated my PTSD from various incidents in my life, producing insomnia, nightmares, and restless sleep. But the silver lining is this: I came to realize that, if it ever did happen that my life might end, I have had a most glorious fifty years on this planet. In a moment of complete uncertainty, I accepted whatever might happen to me with simply—acceptance. And that is comforting, in a strange way—though I am glad it all turned out relatively well, and that the Grim Reaper decided this time to slip away and down the hall.