I (stupidly) tried to introduce a bossy campine pullet to a single ISA Brown hen in a tractor, a few years ago. The campine bit the sexlink HARD on the wattles, several times, hung on real tight looking smug, and then the sexlink proceeded to try to KILL her. I intervened as soon as possible, but not before the sexlink had the campine laid out on her back on the ground, apparently dead. The campine was totally limp, and her legs and neck would wibble very "dead-ish-ly" every time the sexlink would peck or shove her. Seriously, I was totally sure the campine was finis.
I retrieved the campine, and in a few moments she revived.
I do not know whether it was involuntary fainting or having the wind knocked out of her -- that was a SERIOUS clock-cleaning she was gettin' -- or whether it was a desperation attempt to get the attacker to desist. But, it sounds like the same thing you saw with the dog attack. So, yes, it happens.
Hope your other hens are ok,
Pat