Even a many-worlds literalist would require at least one more assumption: that there is a common time flow for all the universes, and that your self-perception is averaged over all of them using some reasonable measure. Note that this is very hard to make consistent with relativity, as in some of the worlds you are spirited away at near light-speed by evil aliens, and the measure of those worlds becomes relatively large once your "stationary" (in some sense) copies die out.