Actually ahayes, it is possible for one to distinguish the difference at the very same time it is happening to one. The Presence is unmistakable (and absolutely unforgettable). The problem is, like "qualia," the experience cannot be directly shared with any other person, let alone be validated by the scientific method.
Once again, how do you determine that your religious experience is true and my sister’s religious experience is false? There are multiple contradictory divine revelations out there and they all have their proponents saying their experience is unmistakable and unforgettable.
This means, I presume, that you've had hallucinations that were not divine revelations. Perhaps you could write a book about how to distinguish them. You could also explain how people who have not shared your "qualia," how to distinguish between others who've had divine revelations from those who have had hallucinations.