One of my oldest hens experienced this 

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May I ask what you feed them?Nothing quite like this ever happened to her before. I remember a couple times maybe earlier this year when she kind of seemed like she's sort of flopped around, but then came back to normal pretty quickly. They eat like Queens I don't understand how they could be deficient in just about anything. It feels more like a neurological thing to me. She is part silky and she does have that kind of poofy hair tuft on top of her head. So maybe it is something that is hereditary. All I can do is feed her the right stuff and pray for her and the rest is up to...... life and death I guess.