The Sun provides life to flowers and to people.  If it is reversed and going down, then its light and warmth is fading … and so is the life it supports.  This is not, as with the blocked card, a suggestion that the life is temporarily gone.  This is a fading Sun — it suggests that the querent is either unable to recapture youth and childhood, or that they are refusing to see the light.  There is a suggestion here that they would rather be in shadow than see what the light might show them.  It is possible that the querent is rejecting reason and logic.  Or, that the querent cannot stop the light from fading.  Ignorance is winning, as are the dim and short-sighted forces of cynical adulthood.  No one is listening to youthful protests, or thinking of the children, of future generations.  Energy fades, the light fades, music and wisdom fade.  Something must be done before all the flowers have wilted away.