This is a newish one, from mid 2010’s.  I saw a preview on YouTube, two different previews actually.  In the first, which made me want to see it, a little girl is taking flowers from a pond in a forest and placing them next to her mother, who appears to be sleeping.  Eventually she stirs and the camera reveals she is dead, and some giant carnivorous worm is chewing on the back of her head, but the sequence is revealed to be a dream.  In the next preview, it just shows a badly washed out dark muscle car driving with tinted windows, and the film’s creators talk about a car with the ability to cause dreams, and say the movie isn’t really a horror film.  Not sure if it ever even got released.

A year or two ago I saw a trailer on YouTube for a movie that looked awesome.  A little girl was singing and scoops a water lily out of a pond and goes through a door that leads into a forest.  It becomes obvious that she’s in a dream world.  She puts the flower next to a sleeping woman who moves ever so slightly.  Then the camera shows behind the woman’s head and it’s clear she’s dead because some giant toothed worm or centipede is chewing on the back of her head.  Then I saw another trailer for the same movie where the filmmakers were saying it was about a car that caused dreams, and the trailer just had a black car driving in a sun-bleached clip that was really boring.  I always wondered if the movie came out, can’t remember what it was called, and whether it had more of the first trailer’s kind of scene.