poorly chicken symptoms, any ideas?

Aw!  sorry to hear of your troubled hen.  How old is she?  we recently lost two of our hybrids to different things, but were told by the breeder that two and a half years is really good for those types (speckeldy and warren).  It may be that she's worn out from egg laying

Hope others can help with a bit more info.
C

Have you checked for all the usual suspects?
Worms - when last treated with flubenvet?
Mites - look at end of perches
Lice - look at vent area and under wings
Is she laying?
Have they got plenty of room?
Being bullied?

One last suggestion - they can get ear mites and head shaking is a symptom - I think it's quite uncommon, but if you've ruled out the more usual problems above it might be a possibility, in which case it's a vet visit I should think. Keep us posted and good luck.