Arelith

As title. The Feylock Sleep doesn't break Invisibility if they're too high of an HD to roll for the sleep will save.

I'm guessing the Invisibility spell isn't counting that touch attack or Eldrich Blast damage as something to break Invisibility over.

-and against a High HD Target, the spell otherwise does nothing.

As an addendum, the same seems to be true of using Sleep on Neutral NPC Monsters, like animals. They'll take EB damage, but will not go hostile.