That's been my going theory. Bleedover from other realities. I'm thankful I've never dreamed first hand some of the ones I visited.
There's some other implications from my dreams, both from dreaming first hand and seeing the result from that dream. You can never fix a timeline. Rather, if you go back to say, stop an assassination that led to your people being exterminated, you can save one timeline, but your own still exists, you just created a branch where those events never happened. (I first dreamed the outcome, then later dreamed about my future self that sent herself back to my timeline by swapping her mind into my younger body and vice versa)