I'm not having much luck finding a thorough symptom checklist anywhere on the web. The pullet is about 4 months old, vaccinated for mareks as a chick. Very healthy up till today, she seems very sleepy. Her eyes close and she seems to be falling asleep just standing there. Eyes are not swollen. No injuries. No respiratory symptoms, no warts or anything. I offered bread crumbs and she ate some so she is still eating. ?? We have lost all the other chickens from this hatch to predators, she is the only one left - was planning to show her.