My chicks are 4 weeks old and it was a great day so they spent a few hours outside. I noticed just now one of them now won't open one eye. If I look at the eye it looks fine but she doesn't like me trying to open it. How can I help her. She's not happy about it and won't just up to roost and seems more bothered. She's usually happy and silly but she's pretty still right now. The others are fine and normal. THanks!