The movie starts with a sister and her brother if I remember right, and they see these creatures in the darkness, if I can remember right, the creatures take her brother to their world to do what they do I guess. It goes to the sisters adult life where she starts seeing the creatures again. There are other people who see them too, maybe her friends from her childhood or something. I'm pretty sure they all get taken over the course of the movie. At one point she is driving and hits one of the creatures in her car crossing the road and in another her bathroom mirror starts oozing black goo and she walks through it into there worlf that looks like a black gooey cave full of them but she makes it out. At the end she is in a phycho ward or hospital or something and one of the creatures gets her. Does anyone remember the name of this movie?

Sounds like They, released in 2002:

http://en.wikipedia.org/wiki/They_(2002_film)

A girl experiences night terrors as a child and overcomes them growing up. But then she encounters a childhood friend who speaks of creatures that only he can see that stalk him in the night. There were gooey creatures in the film and she does indeed go to there dimension at one point near the end.

That's it! Thanks