To strike bottom would be destruction.

Those of our arboreal ancestors who struck bottom died forthwith.

True, the shock of their fall was communicated to the cerebral cells, but they died immediately, before they could have progeny.

You and I are descended from those that did not strike bottom; that is why you and I, in our dreams, never strike bottom.
And now we come to disassociation of personality.

We never have this sense of falling when we are wide awake.