I have a hen who is a little over a year old. About two days ago, I was feeding the chickens bread which I do frequently. She ate some, but then, looked like she was choking: opening her beak very wide, would pick up bread and drop it, etc. After a few minutes, she went back to eating. This morning, she did not leave the coop with the other chickens. She is sitting on a perch opening her beak widely like she can't get enough air. She isn't in a nesting box either so I don't think she's broody. She didn't even come out for sunflower seeds so I'm concerned. What could be wrong? and what do I do?