Are Heaven and Hell only states of mind?

From the book The Great Divorce by C.S. Lewis, we find these incredibly insightful words.

"Hell is a state of mind ... And every state of mind, left to itself, every shutting up of the creature within the dungeon of its own mind--is, in the end, Hell.  But Heaven is not a state of mind.  Heaven is reality itself.  All that is fully real is Heavenly. For all that can be shaken will be shaken and only the unshakeable remains."

By this definition, I have experienced Hell plenty here and now.  Every self-absorbed thought I ever indulged and lingered in eventually led to a state of isolation so dark and confined that there seemed to be no way out.  

There is no friendship in Hell.  Others are there, yes, but not friendship, because in Hell everyone's mind is preoccupied purely on himself--leaving no room to embrace others.