Becoming disoriented in flight is one of the most terrifying experiences pilots can have. In extreme cases, it leads to loss of control, controlled flight into terrain or even an inflight breakup. Less extreme experiences lead to pilot deviation or, more optimally and after the afflicted pilot is safely back on the ground, the expense of pursuing an instrument rating.
This is a companion discussion topic for the original entry at https://www.avweb.com/flight-safety/aeromedical/losing-orientation