We have entire genres of films named for such things (thriller, suspense, horror) and in many cases "hard to watch" from an emotional standpoint is one of the ultimate goals of a film maker. The written word has this as something of at least passing importance and there are entire bodies of musical theory dedicated to it (classic earlier games example). As one of of the chief complaints of 3d and 3d headsets are that it causes physical reactions and many of those are easily replicated (indeed you have probably already designed around them as part of your device) you could employ them as game mechanics of a sort (head tracking + screen filter = actual tunnel vision). This need not be straight up sickness (indeed that might not be so wise) but more subtle things like adjusting an annoying noise/high pitched whine in relation to direction (works rather well for the refusal of the call parts of the hero's journey too). So then any objections, moral issues (given the "this new medium is far too realistic" thing has been thrown around probably since radio became a thing and definitely since film became a somewhat more established you might want to be careful using that particular line of logic) or other input you would like to offer?