Microsoft HoloLens Developer???s Guide

People do not expect sudden changes

One of the downsides of Virtual Reality is that people sometimes get motion sickness. This happens when the vestibular system feels movement but the eyes do not see this. Alternatively, of course, when the reverse happens, the eyes see that you are moving but your vestibular system says otherwise. The body will react to this by thinking that something's wrong, probably some kind of poisoning, and will try to resolve this by getting rid of this poison. This is not the kind of reaction you want your users to have when using your app.

When you limit the amount of movement in a virtual environment, users will probably be alright, but still there's a level of discomfort when scenery suddenly changes or when ...