Abstract: Provided is a spatial disorientation (SD) system and method for detecting, analyzing and responding to an SD event. An input routine includes receiving environment data and/or data from a subject within the environment, e.g., true position and orientation of the environment and/or subject. A vestibular attitude calculator computes perceived subject attitude for environment data elements, and may compute a Washout value. A vestibular illusion routine calculates the probability of a vestibular illusion. A threshold adjustment routine adjusts Washout and vestibular thresholds based on subject preference data. Probability and type of an SD event is determined by evaluating the received and computed data. Sensory countermeasures may be implemented responsive to the probability of an SD event. An output routine provides true position and orientation of the environment and perceived subject attitude via an output device; such information may be recorded for post-hoc review, a method of which is also provided.