Visions of Angels Described in Bible May Have Been Lucid Dreams
Well, the idea that people who claim to have seen angels/demons/aliens may have been hallucinating or dreaming or in some kind of altered mental state isn't exactly new (as Hobson says).
My problem with the study is that the subjects were told in advance to think about a story that involved an angel. It isn't that surprising that they dreamed about what they had been thinking about.
I'm guessing that people who have allegedly seen angels, such as people mentioned in the Bible, weren't planning to see an angel in advance. At least, that's how the stories make it out to be.
I have heard of cultures, such as Native American cultures, where people use mind-altering substances to try to force themselves to have specific kinds of visions. I think that would be more in line with what the study is showing.