Indeed - I suppose it could tie in to various Fortean phenomena. Several I can think of off the top of my head are:
a) The people who disappear (we have a thread for them somewhere) - perhaps these have slipped out of our version of reality and into another almost identical one, not even knowing in most cases, or perhaps suddenly finding that certain people/places/events don't seem to be as they were. Perhaps the forgetting part is the brain papering over the cracks?
b) People who you are convinced had died, even to the point of remembering it being on the news, but it turns out they hadn't (for which we also have a thread!) - perhaps this could happen if you yourself have slipped from an almost identical reality where the person really did die into one where they hadn't died.
c) Shops/buildings that disappear (again, I think there's a thread! There's definitely one about a petrol station in America somewhere on the board. It was in the IHTM board, and I think it was called The Transdimensional Gas Station). In this case the building is where it always was, it's the person who visited it that has slipped into a version of reality where it was never built in the first place.
Of course all of these suppose that if people
do slip into alternate realities, they're ones that are very similar to the one they originated in.
Otherwise, if it was that frequent, I reason that we could expect very different variations of human life to appear out of the blue now and again.
Maybe it's something along the lines of the amount of energy required to pass through whatever barrier normally prevents this kind of thing. It would maybe take less energy to travel to a universe which was directly adjacent (and therefore very similar) than one further 'away' (and thus quite different), much as it takes less energy to move an object a millimetre in a certain direction than it does to move it 10 metres.
Getting back to the dream idea, I've pondered myself sometimes about what if dreams in general are glimpses into the memories/lives of alternate versions of oneself? I like the idea, but then dreams where I'm flying like Superman etc. would seem to rule this out
Edited to fix a typo