In other words, our default is to assume that what we perceive to be true is indeed true, unless proven otherwise. There are things that seem real to us at the time, like dreams or hallucinations resulting from drug use, but once they pass we recognize that they never really came true.
Religious and mystical experiences, on the other hand, are often perceived by those who experience them as real even decades after the experience. Anyone who claims against them “perhaps it is a delusion” can equally direct this claim towards the reality he is experiencing at the moment and question it.
But if he does not do so, and does not provide an objective criterion that makes it possible to distinguish between reality and hallucination, then our default is to believe in experiences that seem real to us and treat them as part of reality. Whoever wants to claim otherwise, has the burden of proof.