When I was a boy I often dreamed my little body was flying around different countries or planets. I later found out this is called "astro-travel" and is a very special ability.
As an adult I dream about the future of my life - especially rooms/houses I will later rent or be in. Then years later, when I enter a room or house I "flash-back" to the old dream. In the dream I cannot tell the date or how old I am, so I really have no idea when these deja-vu experiences will happen. They just do!!
Edgar Caycee said we live another life in our sleep - prehaps "unlocking" some of the 90% of our minds we don't use during the day.
The other main thing is I've experienced a hideous animal spirit come to me while my window is open when I'm just beginning to sleep. I've actually only heard it & sensed it outside - (it roared like an angry Puma). I found out you have to invite these in - if you don't they cannot enter your room (like a Vampire). Edgar Cayce said he saw hell was full of these things, trying to drag you into Hell. I really hope they fail.