I had 2 d'Anver hens kept in a cage in the house. Fed layer crumble and straw in nest box. Poo has been normal and they have been eating and drinking okay, laying about every other day. Daisy seemed sluggish this morning and comb was a little pale. I just looked over and she was in the nest box with her head rolled straight back touching her back struggling to breathe through what sounded like fluid. She then started to thrash around and of course we ended her suffering. I just held her a few hours ago and her breathing was fine. She has been a little fluffed for about a week now but would perk up after being outside for a while so I thought maybe she just needed more sun until today and I thought maybe worms and was planning to treat tomorrow. She had fluid leaking from her vent but only just now. She hadn't lost any weight and no discharge from nostrils or anything. Any ideas on what could have caused this? Her coop mate seems fine but if I can figure out what it was maybe I can treat Rose if she starts to show symptoms or any of the others.