The experiencing that is you, vivid and alive in every way and fully present here and now. For the person next to you it is the same kind of thing, perhaps even more vibrant in some respects, but you have no direct access to it. These two worlds are two facts about the underlying world as you understand it. There could be another next to you whose experiencing was almost identical to yours, was in fact exactly what your would be if you were located in that particular spatial niche with another externally identical to you in yours. These are still two separate facts in the world. This means that nothing in your experience corresponds to what you are as ultimate subject. If you could be copied perfectly, made of the same biological stuff which we know to be replaceable piecemeal, then you could die and be replaced by a copy and none of your nearest and dearest would know the difference. If time is real then the same ought to apply to yourself shifted in time - it's just like you but isn't you, is somehow someone else. These are all simple enigmas, but they have no simple solution. At any rate it's not the ineffable 'feeling of experiencing this or that' that is in question but the 'who' of the experiencing, and the nub of this mystery that remains after unravelling the grammatical solecisms that accompany this question.