Can it raise it's head up when you pick it up?? I'm wondering if it's head is down because it's not feeling well or if the head is "stuck" that way, like wry neck or an injury....
Look up Wry Neck on this site and see if the symptoms match your chick's. If so, you can probably turn things around with speedy treatment. We had a two week old that developed Wry Neck and although it took nearly a week of eye dropper feedings of baby vitamins without iron and egg yolk, our chick pulled through and is one of our more dominant chickens now. Good luck!