I believe in our sleep, we are at one with the multiverse, with our soul in it. And that soul is fractured throughout many universes. Many universe also exist where we happen to not be alive at this moment in time. Many universe also exist where we happened to have been born into existence as lifeforms (whether human, some species we do not know about that evolved in another part of the universe, or some other species of nature on Earth) most likely at a different point in time and space.
This belief was largely triggered by several dreams I had. My elderly dad (73 years old) has senile dementia and my mother cares for him. He sold his house in 2009 (a couple of years before the stroke which triggered the onset of vascular dementia - the house I grew up in). Why am I telling you this? Because just over a week ago, I had a dream that I woke up in this house we used to live in - in the middle of the night. And my dad was wandering around outside, banging my neighbor's fence & door, and causing a disturbance. Myself and a sibling woke up and, in a humiliating experience, dragged him inside and got him back asleep.
The sheer lucidity of this dream, the accuracy of little details such as the neighbor (a middle aged woman) and her garden having slight differences, but all logical & stable rather than anything sporatic or impossible you'd expect from a dream, led me to believe that this dream was in fact a window, some sort of connection on some quantum or other currently-inexplicable level.
As a conclusion, I've come to suspect that parallel universes exist, with slight differences (I believe not due to the natural universe itself, but due to tiny differences caused by impacts from other universes such as stray matter that over time manifested itself as larger differences, yet still insignificant in the grand scheme of things). For example, if a hunk of rock escaped the gravitational pull of anything in our universe from being on the outer reach of its big bang impact, strayed for a long ass time, then reached some other universe, it could have small cascading changes over time, sort of like the 'butterfly effect', AKA the trope of people travelling into the past and stepping on a butterfly only to cause substantial changes eons into the future. As these differences would be slight, and from my dreams, I've concluded that we could be alive in many of them. As for the darkness that fills our dreams/ sleep state, I believe that could be windows into the universes in which we are currently not a life form. Some people experience dreams more often than others. These people could by quirk/ chance, simply have more probability of higher likelihood of being existent at this moment in time. (Time is one factor which I believe would not be changed in any universe).
What I'm getting at is that I figure all universes start off the exact same (enough matter converged at a tiny point in space causing an explosion or 'big bang' due to the sheer compaction of subatomic (or levels less than we've discovered) particles. At this point, they're all the same. Because science doesn't work with ~tilde signs in terms of numbers. For example when we think of melting points, boiling points, they're pretty solid figures. Nature & sub atoms/deeper have to exist like this, or the universe would be chaos & life probably wouldn't exist.
Then, although all universe begin the same way, at some point, stray matter floating through space (from earlier universes in other positions in space) ((position is irrelevant to the state of a universe because all is just empty space, but relevancy comes into play when stray matter comes from other universes in specific directions) can cause and impact at infinitesimal points, areas, and time - changes.
The grand conclusion from my dreams as well as my thoughts above is that we have many, many lives throughout the cosmos, and they're all linked somehow. Although I used the word 'soul' earlier in the post, I hope you don't mistake that for any belief in any deity. But I do believe there is at some quantum or otherwise unknown/ undiscovered level, a bond or common identity/ factor between all of our current existences throughout the cosmos (as well as past and future ones).