I have a single D'anver chick from a hatch. Hatch date Feb 13. Egg from ebay seller. It has been healthy so far and very active until today. I am new to chickens so I need some help figuring out what is up. The chick will fall over and fail around with wings out. Peeps in distress and pants. Does not seem to be able to coordinate legs. Once this "fit" passes the chick can walk normally and acts normal. One of these 'events' happened about 10 minutes ago but now it is acting totally normal. This is the second time I have seen it today. The only thing I have found that seems near the symptoms is Avian Encephalomyelitis. This chick is not vaccinated against Marek's. I only have 2 other chickens, Light Sussex hatched around Thanksgiving. They are outside in the run and have not interacted with this chick. They are fine. The older ones are vaccinated against Marek's - I did it myself. Am I crazy? Is this something? I am mostly worried about it being something that my older birds can catch. I purposefully hatched my own chicks to avoid disease.