I briefly remarked on this phenomenon earlier, and someone said, "Define 'suck out your soul'."  Well, it's mainly a tactile thing: you can practically feel the pulling sensation, if your dreams wander too far into the Future.  It's like something out of H. P. Lovecraft:  The Call of Eutopia.  A professional hazard of having to stare out into vistas that humans were meant to gaze upon, and knowing a little too much about the lighter side of existence.

Interstingly enough,Lovecraft wrote a story that I think captures this phenomena quite well. See also this story, in which Lovecraft briefly revisits the protagonist of the original story, and elaborates on his fate. Of note, both stories deal with seduction by memories of a idealized past, rather than imaginings of an idealized future, but I think that the same general principle applies.