However, as the patient for example turns his or her head to the right in FIG. 5 and the forces applied by side straps 13L and 13R become unequal (i.e., the force on strap 13L becomes greater than the force on strap 13R), the rigid plate 9 actually rotates about the axis 65 (see FIG. 2) extending through the detent-channel locations at B and C. The right side portion 23 and detent 39 of rigid plat