As I already suspected your head bone is not connected to the neck. Besides that your whole armature is quite messy. There are many other occasions where bones aren't connected to anything (legs, feet) and many of them are redundant (in the image below I tried sorting the bones and moved them away for that purpose. I stopped at the neck ;-) ).
Go check your arm bones, there are layers upon layers of bones that don't serve any purpose.
I would start from scratch and slowly by creating the body armature first and then adding the facial bones to that. A good starting point to learn how to rig a character from scratch is Darrin Lile's tutorial. He knows exactly what he's doing and he also has another rigging tutorial in which he uses rigify.
It's also highly advisable to switch to octahedral and x-ray mode when working with armatures (at least until you know exactly what you are doing). It's way better to keep track of your bones and their connections.