In addition to the direct symptoms just listed, several other phenomena are closely associated with motion and VR sickness, and potentially persist long after usage. One of them is Sopite syndrome , which is closely related to drowsiness, but may include other symptoms, such as laziness, lack of social participation, mood changes, apathy, and sleep disturbances. These symptoms may persist even after adaptation to the systems listed above have been greatly reduced or eliminated. Another phenomenon is postural disequilibrium, which adversely affects balance and coordination . Finally, another phenomenon is loss of visual acuity during head or body motion , which seems to be a natural consequence of the VOR (Section 5.3) becoming adapted to the flaws in a VR system. This arises from forcing the perception of stationarity in spite of issues in resolution, latency, frame rates, optical distortion, and so on.