Motion sickness considered as a movement disorder

Motion sickness typically is associated with motion of physical or virtual vehicles. However, the symptoms that are associated with motion sickness also occur in other situations. Under classical theories of motion sickness etiology, these other situations are interpreted as not inducing motion sickness; that is, the symptoms are attributed to different causal factors. In this article, I review situations that are characterized by motion sickness-like symptoms, and I suggest that they share a common etiological basis in unstable control of posture. The postural instability theory of motion sickness etiology argues that motion sickness symptoms are a consequence of instability in control of the body and its parts. Within this theory any circumstance that gives rise to unstable control of the body and/or its parts can give rise to motion sickness symptoms. I argue that postural instabililty may arise in physical and virtual vehicles but also in other situations. I suggest that the symptoms associated with these situations may be caused by postural instability and that, accordingly, they may constitute instances of motion sickness. For this reason it may be appropriate to classify motion sickness as a type of acute, transient movement disorder.