...Hearing the "clink" sound of a glass plate falling out of the holder when you're trying to reinsert the dark slide?
I was lucky and had only 10 minutes walk to get back to my darkroom. Carried the camera very carefully, back down inside the darkcloth back to the darkroom, removed the lens, pushed the plate in with a finger through the lensboard opening, inserted the darkslide, and finally started breathing again.