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.