If you have a chicken acting strangely, like putting their head between their legs, jerking their head, skygazing, or acting paralyzed, it is possible they have a selenium deficiency.  This can happen at any age.  Just get the suppliment in any store, grind it up and add water.  You should see improvement in a few days if that is the problem.  Silkies seem to get this often.  I know when I was looking for a cure, I couldn't find this information anywhere, another breeder told me.  Good Luck!