Methods for detecting and mitigating conditions associated with motion sickness and visual fatigue for users of augmented or virtual reality systems include receiving, during operation of a head-mounted display device, sensor data from inertial measurement unit sensors of the device, determining, dependent on the sensor data, that a condition associated with motion sickness or visual fatigue exists, and modifying, in response to determining that the condition exists, an operating parameter for the device to mitigate the detected condition. The sensor data may include acceleration data with respect to six degrees of freedom. Detecting a condition associated with motion sickness or visual fatigue may include comparing change rates for the sensor data to predetermined gradient thresholds. Modifying an operating parameter may include changing a rendering resolution, a spatial quality setting, or an effective field of view to, at least partially, mitigate the detected condition. The method may be repeated periodically.