Not sure. She has always been one of the more docile girls in the flock. I started worrying about her yesterday. I lost one on Thursday, so this is not a fluke.
Based on Eggcessive's advice on my post (thank you!), I will start treating with corid tomorrow.
I am interested as well - I have one that is lethargic. I have her in a dog crate in my house.
Any chance that there could have been fumes in your garage? I believe that birds are very sensitive to air quality.