older hen is acting disoriented

[smiert]

This hen is a few years old. She is acting strangely, sits in the same place, doesn't move around much, has watery diahrea, Her head is constantly bobbing up and down. She acts as if she is snapping at invisible flies. She has no respiratory problems that I can discern, no sneezing, or coughing,or raspy breathing. I've been giving her some polyvisol vitamin drops and yogurt mixed with her feed. Any ideas? This has been going on for probably 5 days now.