I am new to raising chickens. I have 4 chickens that are about 8 months old. One of them is acting very listless. She sits down when eating, as if it's too much effort to stand. Today she is lying around the yard instead of just sittling, like when she suns herself. My chickens usually hang out together but today she doesn't seem to want to go see what everyone else is doing. It' very unusual. I haven't seen her run after the others, instead she very casually walks from place to place. Otherwise, she looks ok. She has all her feathers, her eyes are clear, no nasal discharge or cough, and when not lying around, her tail is high. She only started laying about 2 months ago but stopped several weeks of eggs. I assumed it was normal because of the shorter days as one of my other chickens stopped laying too. Please help!