If a pilot develops spatial disorientation, then there is a risk of a crash. It can affect a person flying fixed wing aircraft or helicopters.
Spatial disorientation results in the pilot being unable to determine location, altitude, speed or attitude.
Risk factors for pilot disorientation:
(1) no or low visibility
(2) poorly designed or malfunctioning flight instruments
(3) illness or drug that impair vision, vestibular function or other sensory perception
Factors that can reduce disorientation:
(1) pilot training (simulators, etc)
(2) physiologically efficient ground lighting