The skeptical Dream argument appeals to the possibility of dreaming. The skeptic holds that states of being awake are subjectively indistinguishable from possible dream states and that this means that we do not know that we are awake. This, the skeptic then claims, means that we have to accept that we do not have external world knowledge.
It is natural to assume that there must be a connection between the Dream argument and epistemic internalism, the view that a belief is justified for a given person if and only if the person has cognitive access to all the factors that are needed for the belief to be justified. The problem, the skeptic thinks, is that in order for my belief that I am awake to be justified I have to have cognitive access to something that establishes that I am awake. But according to the skeptic, even if I am awake, this is not something I have cognitive access to. However, the more precise connections between internalism and the skeptical argument are not so clear.