Hi,
you could try doing a search on the databases (pubmed). Look at the journal cephalagia.....all about headaches. You could look up the diagnostic criteria, compare to cervicogenic headache etc (Sjaastad et al, 1998, Headache)

You could also try looking up work by Beeton, Jull etc on deep neck flexors with reference to physio and treatment interevention.'

Hope this helps ( I'm at work or would look up those references for you..)Good luck, Sam