Regardless of any other issues, this sort of thing DOES happen. Back during the Korean War, my Dad witnessed just such from “a big tough Negro dude” (’70’s verbiage from my conservative white Dad) when he and BTND were in line to get some shots for Army duty. The setup was that as the line moved forward, the soldiers got jabbed in both upper arms simultaneously. BTND was immediately ahead of my Dad. Somehow the situation was such that this poor fellow did not get a clear view until he was seconds from receiving the two shots that were about to go into him: He saw the two big needles and passed out right in front of Dad. Dad and a couple other soldiers got BTND, still “out”, off the floor and into a chair, whereupon the shots were administered. A nurse showed up to begin to revive BTND, while Dad and the others went on to get their shots and then go to whatever the next step was...
Ah, I miss Dad. He could recall stuff like this and have US on the floor in his retelling. Still conscious, though. :-)
My dad was in the Army in the early ‘50s, too, and told me about one of the recruits fainting. I went through that line for shots in 1989, at the age of 31 (went through initial training later than others). The place for getting vaccinations, uniforms, etc., was called “Reception Station,” just before basic training. None of the young men around me fainted, but one of the shots was a large syringe of penicillin to the buttocks and left a little streak of blood running down. ;)