I’m looking for that movie.
I only remember that a young boy makes an accident and loses his consciousness.
then his ghost goes to his mother and talks to her but she can’t hear it saying “I’m lying in the mud”.
then the mother realizes somehow and searches for him.
The Invisible (2007)
https://www.imdb.com/title/tt0435670/
Found it, thank you.
Here’s the scene
Sounds like a Solve for SS.