This whole discussion is essentially a reiteration of Descartes, except he flips the perspective from I think therefor I am, to I am therefor I think.

 In the words of the poet Rimbaud, however, "One should not say 'I think,' but rather 'I am thought.' 'I' is an other." In this perspective, existence, and consciousness of existence, Being in the Heideggarian sense, 'is' only insofar as it refers not to an external object but rather, as it refers to an Other which gives 'Self,' or 'I,' meaning through differentiation from the object or other-than-itself. From this perspective, there can only be a "hallucination" of your conscious reality insofar as that "hallucination" is thought of by another person, which, by the process of being thought of, makes what is being thought of a reality to the 'Self.' The characteristic of being thought of implies that the other imposes its meaning on the self as different, and, therefor, what is thought of cannot be defined as a hallucination as "not real," because it exactly presents itself as something "real;" as against or alongside that which is purely subjective or potentially imagined.

Essentially, what I mean to say is that we cannot realistically or logically differentiate our own perspective or selfhood from our experience of others, which undermines the perspective that Consciousness is a phenomena created purely by ones self or ones "own" sensory experiences. I desire what they're eating because they have it, and not because I desire the object, or experience of the object, that creates their satiation. I desire the object because they make it look satiating, and they make it look satiating because they know I will desire what they have if they do.