I had a roo do the same. Ues Vit E. Of you have the human form crush it and feed it directly. Thats what i did. We called him our stunt double rooster lol .
I do agree that what he is exhibiting is neurological. Wry Neck is a symptom that can be caused by vitamin deficiency, head/neck injury and certain diseases like Marek's.
I would also weigh him to get a baseline weight and monitor him closely for any weight loss. He does appear to be "eating" in the video, but I suspect he is keeping up appearances. Check his crop each night to see if he has anything in it.