First please try to recenter head tracking, either from the vorpX menu or with ALT+SPACE.
If that does not help, check whether you maybe have any peripherals like a flight stick or driving wheel connected. If so, disconnect them for testing purposes. Since on flight sticks and driving wheels some axes aren’t always centered (e.g. a throttle), vorpX’s gamepad > mouse/kb mapper with a bit of bad luck might translate such a non-centered axis to mouse movement.