I have a buff Orpington hen who is about 4 years old & I good health. Last week I noticed she seemed stress which I thought was due to extreme heat & brought her inside for a few hours. She seemed fine but I noticed her laying down a lot the next day; then noticed she can only take a few steps at a time then lays down immediately. I checked for bumblefoot & treated for mites, even though so sign of. Her legs & feet do not appear to be broken or swollen. She is eating and drinking & looks alert. I have one other hen who is acting completely normal. Any ideas what the issue could be??