(There is an extensive discussion in recent philosophy about how exactly unreal events like these can still trigger something resembling authentic emotions, how you could be, as in the title of one influential paper, "fearing fictions". The central question here is why an emotion such as empathy for Desdemona or anger at Othello is felt in the audience but doesn't, as it would in real life, trigger any action at all. Why do emotions in the real world motivate us to do something whereas they simply leave us transfixed and immersed when we're at the theatre or in the cinema?)
In that earlier post I looked at spatial relations and the notion of a point of view. There is, however, also a connection to what I've called aesthetic ascent.
That we can see things thus in two different ways (the world of the play: Othello, the palace, the strangling vs. the real world: actors, a scenery, and acting) is a condition for making the step from immersion in the world of the play to the levels of comparison and appreciation. We can only begin to compare Shakespeare's play to other plays with similar plots, or the particular stage design to that of other productions, or these particular actors to others doing the same part, if there is some discernible difference between, say, watching Othello strangle Desdemona and watching Sir Laurence Olivier and Dame Maggie Smith acting — performing that strangling scene in act V. (It seems that Williams was able to do so; nowadays, our only chance would be on video.)
Even though the world of a fiction can have our full and undivided attention at the level of immersion in the aesthetic ascent; even if we might, for a period, use our capacities of perception and imagination exclusively following the plot of a novel, play, or movie (and, in a more general sense, even a dream, a scenario, a memory or a future plan); even if nothing about the real world occurs to us for quite some time (such as our sitting in a theatre seat or reading chair, the fact that there are other performances of that same play, different tellings of that same story, varying interpretations of what's going on or how it might sediment itself in reality) — even so we are never part of that fictional world; we're in the real world, and thus can never be in the world of an instance of unreality.
At the same time, this apartness is the basis for aesthetic ascent: leaving the level of immersion and comparing that which is going on with other, similar instances. Making this step means to switch between the two ways of looking at things Williams distinguishes: switching between seeing the palace (when immersed) and the scenery (when comparing).
 Bernard Williams, "Imagination and the self", in: Problems of the self. Philosophical Papers 1956–1972, Cambridge: Cambridge University Press 1973, 26–45, 35.
 Kendall Walton, "Fearing fictions", in: Journal of Philosophy 75 (1978), 6–27.