I think we enter the thought-universe at night when we dream. Still tethered to our flesh, but only partially. And when we die the tether is cut, we drift into large strange places and dream for a million years (if time is even a thing there)

But ya, we invaded this world through incarnation in bigbrained apes. Then forgot why we came.

(A brain, or the thoughts in it, is a pretty good physical simulation of our native land)