I have a barred rock, approx 3 weeks old. He is in a little pen with 5 other chics the same age. About 3 or 4 days ago it started acting funny. Its like he has lost control of his body. His legs are spread straight apart and its like his head has spasms. His head shakes back and forth real fast for 4 or 5 seconds then stops for a minute or so then does it again. He is still eating and drinking when he can stand up to do it. Any ideas?