My 2 week Delaware chick is acting very strange. All day, she has been tucking her head all the way under her belly. She will get her head so far under her belly (while walking backward) she will literally do a front roll and land on her back. When she is walking backward it looks like she has no head or neck. I checked for pasting thinking she was trying to reach her vent, but all is clean. She is not pecking at her feathers, just this weird tucking. She is doing this over and over. She is a little lethargic, but when I rouse the flock she will walk around normally and eat and drink before resuming the behavior. She even sleeps with the head tucked under. Any ideas?