i have week-old chicks and one is sick. it was fine last night, but this morning it's sitting down with it's eyes closed and breathing heavily with his mouth open. the other chicks are fine, and no one has a pasty butt. they're in a bin with a heat lamp, and on newspaper with hardware cloth for traction. they have food (chick starter) and water, and i clean out their house every day, so conditions are good. does anyone know what may be wrong with my chick?