Hi,
some time ago I did a little experiment to distinguish fantasy of reality when in a state of daydreaming or imagining. At first I thought it was not very meaningful, but I've changed my mind and think it maybe could be interesting for some.

I got a phone call of a friend who had trouble with some, let's say very unpolite guys. That lasted on my mind and I found myself often daydreaming about it that day, in those daydreams I helped my friend, I was strong and had guns you know this kind of stuff. When this also happens in a meditation, I wondered: "Look look, this fantasy-visuals are quite similar to your mind journeys. So when you think this is fantasy, what about your other trips?" I then had an idea. What would happen if I would invite a helper into this crime-scene I called fantasy? I then let this scene build up again, me the tough fighter facing those nasty guys. Then I invited a helper. A fuzzy figure appeared which I acknowledged as a helper. I made a sign that I allow the helper to interfere, and the helper sort of pointed at those guys and it made a "puff" and they were gone.
I found that quite natural. I realized through this that I unconsciously knew the difference of fantasy and nonphysical reality, but had to work on bringing it into awareness to gain certainty and to act more effectively in my mind-journeys. So, anyone could try this method with inviting a helper. It may be good to observe the differences in the appearance of the helper and the fantasy items, the difference in the feeling you have with them. Then, you can try to observe what in a scene which you question whether it is a kind of reality or fantasy is persistent when you attempt to change it and which is not. Things you can easily change are probably not real, as the term "real" has in it the meaning of independence from yourself to some degree. It might be that some things might be changeable in a scene, but others not. For example, when you see a person, and the look of the person changes, maybe from young to old, the clothing varies etc, but the feeling you get from the person remains, for example a sadness and a feeling you're on a mission to help this person, then I would not discard it all as fantasy, but take it as partly imaginated by you, which can be a tool to perceive out there as we like to have something familiar to deal with, but the remaining, which doesn't easily change, or which you feel a resistance within yourself to attempt to change it, I would interprete as the real part of the scene.

This should also help for looking back on mind-journeys. The point is, when you feel you couldn't or wouldn't change things in those experiences, then it's more than fantasy.

Something left to ponder is the distinction of personal/internal reality, for example persisting fears, habits, aspects etc. and "outside" reality meaning other beings are involved (like for example in a partnered exploration).

There also are places we can create with imagination. They can be easily changed because you are the creator, but nevertheless, when often imaginated and visited, those places seem to gain a sort of reality, to a degree that you even find details there you can't remember to have created but are fitting well with the rest. Also after some time you might realize it's getting more difficult to change those imaginated places the more often you frequent it.

Spooky