One of my chickens is free-range. Untill now she has been happy and healthy, but the past few days she hasn't been acting the same. Usually she is very active, but now she just sits in one place and doesn't move a lot even when I come very close to her. She looks like she is sleeping. I can't see anything that looks physically wrong with her but i'm definately not an expert. Does anyone have any idea what could be wrong with her? Thanks in advance for your help