Begin by sitting in a chair with good, neutral posture.  Your shoulders should be over your hips and your head should be facing straight ahead.

As with the retractions, retract your head as far as possible.  If you cannot get to full retraction without pain, go back and repeat the cervical retractions until you can achieve full range without pain.

With you head retracted fully, slowly allow your head to fall back over your shoulders.  The goal is to get to full range of motion without pain.  If you experience any pain, stop at that point and return to the starting position and begin again.  Repeat the entire procedure as directed by your physician or until symptoms abate.