Most problems related to disorientation can be traced to the inner ear, a sensory organ about the size of an eraser on a pencil.
The inner ear is similar to a three-axis gyro. It detects movement in the roll, pitch, and yaw axes that pilots know so well. When the sensory outputs of the inner ear are integrated with appropriate visual references and spatial orientation cues from our bodies, there is little chance to experience disorientation.
The problem occurs when the outside visual input is obscured, leaving just the output from the inner ear — and that's when trouble can start.
A pilot suffering from spatial disorientation has difficulty in determining how they are flying in relation to the horizon.
Fluid in the inner ear reacts only to rate of change, not a sustained change. For example, when you initiate a banking left turn, your inner ear will detect the roll into the turn, but if you hold the turn constant, your inner ear will compensate and rather quickly, although inaccurately, sense that it has returned to level flight.
As a result, when you finally level the wings, that new change will cause your inner ear to produce signals that make you believe you're banking to the right. This is the crux of the problem you have when flying without instruments in low visibility weather.
Even the best pilots will quickly become disoriented if they attempt to fly without instruments when there are no outside visual references. That's because vision provides the predominant and coordinating sense we rely upon for stability.
The obvious method to prevent disorientation is the instrument rating. But, that rating alone is no automatic guarantee, because there is no such thing as "knowing how to fly on instruments."
Practice your IFR skills - you are either trained and current, or you are unqualified!
(Acknowledgements: Goldi Productions Ltd.)