Cervical extension is an important movement that allows us to look up without putting stress through the upper and lower back. If you do not have adequate cervical extension, you may be compensating by using your available thoracic and lumbar extension, and putting strain through the musculature in your spine.
To learn how to assess your own neck mobility, check out our post from 2 weeks ago: http://ascentpt.blog/2014/02/13/how-is-your-neck-moving/ Cervical extension should be within about 10 degrees from parallel.
If you are limited in extension, you can try this self-mobilization with a towel. Place a towel behind your neck, just below the base of the skull. Pull forwards with your hands on the towel and gently tilt head up, keeping pressure on the towel. Hold for 10-15 seconds, and repeat 5-10 times.
A video of this exercise can be found at http://www.youtube.com/watch?v=SYm6b6XEcSo
Do not continue this exercise in the presence of sharp pain, numbness/tingling down either arm, dizziness, nauseousness, blurred vision, or severe headache. If you are having any of these symptoms, you should see a physician.