I don't think it was the Wii fit. In fact I'm fairly sure that it wasn't. However, the bottom line is that at the moment my neck doesn't work properly. I'm moving a bit like a Cyberman, turning my whole body to face people rather than just rotating the head part. Looking slightly to the right is fine, looking more hurts like heck. It seems to be easing a bit, but I've been playing GTA 4 rather than exercising.
Just in case.