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In all probability this is neck
stiffness due to wrong sleeping posture. Other than that
it can be occipital neuralgia which results from compression of higher cervical vertebral nerves. It can also be due to an inflamed carotid artery
or jugular vein.
It is difficult to comment beyond this at
this stage without examining. Please consult your PCP for primary examinat
ion followed by proper investigat
ions and referral. Hope this helps. Take care!