I am having a similar problem with my silkies right now. They are all about 8 months old. They are housed inside due to the winter weather here in WI, although our winter has been rather mild until yesterday...-7 this morning! Anyways, I went out to feed the silkies and one of the blacks was dead! No warning, no symptoms, nothing. the other 7 birds seemed just fine.
2 days ago, my husband went to feed them, and found Peanut (the small white one) upside down on her back. But he picked her up and she was fine. Now this morning, there she was on her back again. I brought her into the house for the day and gave her some electrolytes. She keeps leaning to one side...seems to be losing her balance. I just don't get it! I haven't brought any new birds into their coup since September and like I said they have been confined all winter.
What gives? I hope it isn't the dreaded Merek's. I am going to try and give her some B vitamins tonight....got nothing to lose I guess. Sigh.