Modern day sedentary lifestyles include lots of sitting at computer screens which can bring about poor head and neck posture. This can result in muscular fatigue and neck and shoulder pain.
Try this Exercise to Learn to Lengthen the Back of the Neck and Improve Head and Neck Posture:
Lie on your back with the hips and knees bent. You can place a thin towel/cushion under your head if you feel that your chin is poking upwards. Feel the bony area at the back of your head contacting the mat and then lengthen this bony part of your head away from the base of your neck. Hold the lengthened position for a moment and then relax. Repeat this process a few times. The movement here is very slight, in fact place your fingertips on the muscles at the front of the neck to check that they remain soft.