I remember a similar problem with my Reverb G1. Every once in a while, my head would seem to lock in position, and if I physcially moved my head TOWARD the instrument panel, the panel would move away from me.
I would try to shake it off by looking over my right shoulder, center ing my head view, then my left shoulder, center the view, then back again. Then sometimes it would just correct itself.
I suspected finally it was a tracking issue with the unit itself - be sure your room is well lit to help the tracking cameras - and eliminate sun glare from windows, etc.