Cybersickness While Lying Down in Virtual Reality: Conflicting Theories of Sensory Conflict and Postural Instability

The rapidly changing future society is making the use of virtual reality (VR) in a lying posture increasingly important, considering the ever-expanding user base and the growing tendency to seek casual usage. However, cybersickness can still be induced even in a comfortable lying stance, which presents a conflict between the sensory conflict theory and the postural instability theory. To examine these competing explanations, a VR exposure experiment lasting 3 min was conducted with 36 participants in an environment where body posture and view orientation were systematically manipulated. Objective metrics, including heart rate and eye-tracking indices, were included alongside subjective questionnaires to evaluate the level of cybersickness, presence, and task load. Through the analysis, Fowler’s position was identified as the most favorable physical configuration for mitigating cybersickness. It was demonstrated that when Fowler’s position is combined with full forward view reorientation, postural stability is maintained and sensory mismatch is minimized, thereby maximizing VR comfort and usability in a reclined state.