For every inch your head is forward, your upper back and neck muscles have to hold an extra 10 lbs (~4.5 kg), as they have to work harder to keep the head (chin) from dropping to your chest. This also forces the sub-occipital muscles (they raise the chin) to remain in constant contraction, putting pressure on the three sub-occipital nerves. This nerve compression may cause headaches at the base of the skull or mimic sinus (frontal) headaches.
Kapandji, Physiology of the Joints, Volume III
We address this in two ways at Denver Chiropractic Center. We use chiropractic adjustments to realign the spine. We also use Active Release Techniques to release those tight sub-occipital muscles that can cause headaches, neck pain and fatigue.