Yesterday all of our birds seemed fine. Today I went out to collect eggs and a few were sitting in the nesting boxes. I put my hands under their bottoms to feel for eggs like usual and when I did I realized that one of them was a 36 week old Wellsummer whose eyes were shut and there were no eggs under her. When pushed her to the side to feek for eggs she fell over and started twisting her neck and her feet were curled up. I took her out of the coop and she seemed to not be able to control her head or legs and her wings would occasionally flap then she would lay on her side with a wing extended. I was trying to figure out what to do and she died right there not 10 minutes after I found her. I know for a fact that this bird was acting like her normal self yesterday. She didn'l feel malnourished or have any visible symptoms. Does anyone have ANY ideas? Our other birds seem ok. The neck twisting had me thinking Marek's, but she was a vaccinated chick and our whole flock was vaccinated as chicks so I am not sure that could be the case. Anyway, just wondering since I never had anything like this happen before, and so suddenly.