UFO book reading recommendations

A bit on the fringe even in UFOlogy, I am reading about "Men in Black" in some books by Nick Redfern. He is a really good writer and I almost can't put down the books. I was a bit surprised by the spiritual component in Men in Black. People see them in dreams as well as during sleep paralysis (I heard of people seeing a "hat-man" during sleep paralysis. I wonder if its the same?).