An overview of spatial disorientation as a factor in aviation accidents and incidents2007 Dr David G. Newman"...
Types of spatial disorientationThree basic types of SD have been described, for the purposes of classification. These types are Type I (unrecognized), Type II (recognised) and Type III (incapacitating).
Type I (unrecognized)In this form of disorientation, the pilot is unaware that they are disoriented or that they have lost situational awareness. The pilot, unaware of the problem, continues to fly the aircraft as normal. This is particularly dangerous, as the pilot will not take any appropriate corrective action, since they do not perceive that there is in fact a problem. The fully functioning aircraft is then flown into the ground, with often fatal results. This form of SD is clearly dangerous, and accounts for the majority of SD accidents and fatalities (Braithwaite et al., 1998b).
Type II (recognized)Type II SD is more common than Type I. In this form of disorientation, the pilot becomes aware that there is a problem. While the pilot may or may not be aware that the problem is SD, in this form of disorientation they are aware that something is not quite right, that their sensory system is giving information that does not agree with the information available from the instruments, or that things just don’t add up. The conflict between their own perceptions and that given to them by the instruments or the outside visual world alerts them to a problem, which they are then in a position to deal with. If this is successfully dealt with, a SD accident does not tend to result. The pilot may then have received a valuable lesson on SD and how to recover from it.
Type III (incapacitating)In Type III SD, the pilot experiences the most extreme form of disorientation stress. The pilot may be aware of the disorientation, but is mentally and physically overwhelmed to the point where they are unable to successfully recover from the situation. They may freeze at the controls, or make control inputs that tend to exacerbate the situation rather than effect recovery from it. The pilot may fight the aircraft all the way to ground impact, never once achieving controlled flight. Such forms of disorientation are a result of breakdowns in the normal cognitive processes, possibly due to the overwhelming nature of the situation, especially if other factors such as fatigue and high workload are also present....
…
CONCLUSIONSpatial disorientation (SD) is always a risk to pilots. It is a function of the inherent operating limitations of the normal human orientation systems in the three-dimensional, complex motion environment of flight. It can happen to any normal pilot at any time. There are many different illusions and disorientating phenomena that pilots may experience, depending on the nature of their operations and the phase of flight. There are many steps that can be taken by pilots to minimise their risk of experiencing SD on a given flight, many of which involve pre-flight planning and adequate preparation. Being aware of the risk of SD is one of the key elements in preventing a SD accident."
Source: https://www.atsb.gov.au/media/29971/b20070063.pdf (0.4Mb)