You asked the very question I myself have been wondering for quite some time.
How do we tell the difference between imagined and real ideas? When dreaming, the ideas seem real enough. It is only when you wake that you understand that you had just been asleep and all your "visions" were just a dream.
But what about intuition? That happens while awake, so you can't just shrug it off as 'just a dream'. Are there angels talking to you? Are you psychic? Are you picking up messages sent by others via some sort of telepathy? How do you know?
I wonder too... I still believe in those things but I'm taking a much more detached approach to it. I feel like if I feel out of balance/too fixated it's probably my brain making stuff up. If I feel centered and relaxed about it, I feel like it's more likely to be something I'm sensing rather than something I'm making up because I want it to be that way.
That's probably a good way to do it since our subconscious is likely more in tune with nature and our consciousness is the one that wants things done now.