One of my favorite pullets survived a dog massacre once, and acted very similar, in shock, unresponsive, panting etc. After a few hours she began holding herself upright like your chick. She didn't move for about two days. When she started moving she had a severe limp although no broken bones. About 4 days after she was good as new. Sending well wishes for a complete recovery for yours. My pullet never grew any more after the incident (4 months old) and stayed a tiny bird (she was an Easter egger) but began laying at the same time as the rest of the flock and laid enormous eggs for her size.
Best wishes, Ashly