The Witch In Your Room

The witch is watching you sleep because ...

1. She is a dream-vampire: to keep her powers she needs to drink one dream per night.
2. She needs your breath to build her familiar.
3. She has stolen the skin of your wife ages ago.
4. She met you around  Sirius while you were dancing with the planets. She is here to consume your marriage so she can give birth Them-Who-Come-From-Beyond.
5.  She is searching your dreams for the true form of Leviathan. She doesn't know why your dreams contain her; she only knows they do.
6. You look like the adult version of her child; the one she sold ages ago to the devil in exchange for her powers. She misses you.