Your head is quite heavy and the neck muscles needed to keep it steady have to be strong. Sit up straight in the chair with your feet flat on the floor, your chin parallel to the floor and your shoulders down. Feel the muscles at the back of your neck. When your head is well balanced they will be soft, but if they are tense they will feel hard, ache and give you headaches. Move your head around until you feel the muscles relax, then enjoy that feeling.