JL "And how are we certain that what we dream is actually a
   dream, and not reality? And vice versa."
   I've done a lot of thinking about it. Decades even* :P
   and...
   well...
   there's not, yet ... there also is.
   *
   There's no nowhere. Even nowhere is a somewhere. Reality or
   dreaming, has to take place in a someplace.
   *
   So... even if we believe Leonard Suskind, the theoretical
   physicist (ie: science fiction with math behind it) who says
   that we may be a two dimensional hologram stretched at the event
   horizon of a black hole and that our 3D universe and Time is
   just an illusion of a replayed hologram...
   *
   ...or if we are the dream of the Universe...
   *
   ...or if we really _are_ in our bodies+brains on this planet but
   in a dream state instead of an awake state...
   *
   ...it's still real in some fashion.... even if it's a dream...
   *
   *
   That's the best I can think of at the moment :P