You may have Binocular Vision Dysfunction

In Binocular Vision Dysfunction, the line of sight from one eye tends to be slightly out of alignment with the line of sight from the other eye.  This misalignment can be vertical, horizontal or both and puts heavy strain on the eye muscles as they are constantly trying to correct the misalignment to achieve single focus.  This heavy strain on the eye muscles results in dizziness, headaches, disorientation, neck aches and reading difficulties. These common symptoms are not traditionally thought to be to be associated with your vision but they are. 

There are three forms of Binocular Vision Dysfunction: Vertical heterophoria, Superior oblique palsy, and horizontal misalignment. The corrective measures taken by the eye muscles in order to keep the lines of sight aligned, i.e. vision that is not blurred or double, results in overuse of the eye muscles making them strained and fatigued which results in many of the symptoms of BVD. Head tilt is known to occur in Vertical Heterophoria and Superior Oblique Palsy to minimize misalignment and avoid double vision. In order to achieve single focused vision, the brain takes a corrective measure by tilting the head slightly resulting in neck pain and other BVD symptoms.