When you sleep, your soul briefly returns to the place where it was created/goes to when it dies, and seeks nourishment. Everybody's soul is created with a little link (or you could say a greater entity calls it back) to that place so that it can return easily, but upon death, the soul returns via that and annihilates the link as if returns.
Also, as an added thingy, you could say the entity supplying the link, or residue of the links themselves, (whichever) is the source of all arcane power.
A great treasure has been stolen from the Palace and taken to the nearby Temple to the Bitch-Goddess Atrath Klee. The King demands that the party go and retrieve it - the only snag is that the Temple is guarded by potent magic that will kill any male who steps inside. It's just as well that the King has a stash of Girdles of Gender Alteration for just this circumstance.