"Imagine a universe, like ours, overlapping ours, except where some of its matter spontaneously rips itself apart, and other matter can be mashed together if you squeeze it hard enough." "That's nightmare fuel! Fortunately it's probably impossible, so far as we can tell."
I can imagine other scary thoughts, though. Ever read any Warhammer lore?
On this the same line of thoughts, so far we have 0 proof that all dark matter is _the same_. We observe gravity effects but IIRC they very little tell us about their own homogeneity. We very well could have a few parallel sectors, one of which is ours.
https://en.wikipedia.org/wiki/Hidden_sector
The scary thought is that, were it true that there is voluminous richly-interacting dark matter, we would be the actual dark sector.