Ok, got three of those on the mend. DH massaged throats and crops after using syringe to put olive oil in their throats. One's throat looked twice as big as it should have been. Thought I'd lose him for sure.
What happened was that overnight, they ate all their feed-they're getting too large for 20 chicks and the size feeder, I guess, but they've never eaten that much before so I thought they had plenty. Almost the entire feeder was full when I went to bed. When I refilled it, they all started gorging-it was a madhouse! When I thought, hey, I'd better take this feed away before something bad happens, it was slightly too late and three were gasping for air. Thank goodness I didn't fill it and leave! So, they seem to be breathing okay now, but just very tired. Whew! Tomorrow afternoon, or when the rest of the chicks are gone to their new home, the nursery will be cleaned out and they move to larger quarters with larger feeder and waterer.