My 4 week old Serama chick suddenly is unable to stand. She sticks both legs out straight in front of her and falls back on her butt. She falls over on her side. This morning I found her on her back unable to get up. I have not seen her eating or drinking because she is unable to get to the feeders. I have tried to hand feed her and put her up to the waterer but she will not eat or drink. I have 3 other Serama chicks that all seem okay. But I am very worried this may happen to them since it has a sudden onset. Any idea what this is, why it happened, and any cure?