Lavender Orpington Hen Stumbling and falling over

[akmcgrory]

I have an approx 18 week old LO hen and she has begun tripping over things and falling over. She even will eat laying down, although she is not over weight and feels light to pick up. It has been very hot here and the other chicks with her have coccidosis I believe. I am treating all with sulmet and med chick feed. I also moved their house to another spot in the yard. I had all of them in the garage with the air conditioning on yesterday and over night. Nothing is broken in her legs. She has always been a little strange, but now this. What gives? She is beginning to turn red around her eyes, so I know her body is getting ready for egg production. Could she have heat exhaustion and just be weak? Is the sulmet hunting her? Please help! Thank you!