One of my year old black sex-links is constantly falling asleep. She will walk sometimes with her eyes closed then wake up. Looks like she is exhausted. I have 10 sqft/bird for the coop and they have a 20' x 30' pen. They have been fed layer plus pellets (18% protien). Comb looks good not pale, and I suspect she has not been laying. Last night on the roost her crop was empty. Vent and surrounding feathers are clean although looks like small case of mites where some feathers are missing on her bottom. I threw down some diatomaceous earth a couple days ago to hopefully cure the mite issue. Could her condition be mite related? Any ideas?