While it would seem there are two different things going on (the headaches and the inability to comfortably tilt your head backward) the two could be related, since both involve the blood vessels (especially the basilar artery). There may be an anatomic abnormality which causes the impingement of blood supply to your head/brain when you tip your head back (a not terribly unusual problem), and this may also be contributing to the headaches.
A neurologist should be consulted with an eye toward determining if there is need for additional consult with a vascular specialist, as there may be either a skeletal or blood vessel malformation involved, and whatever is causing this, it needs to be diagnosed and proper management begun.
I hope this is helpful to you. Please follow up with us here as needed.
John Kenyon, EMT, CCT
Non-invasive cardiology tech, Emergency and Critical Care technician, Critical Incident Stress Mgmt. specialist