If he feels anxious, it means that he thinks you are doing something against him.
To explain it with an idiom is to dig your own grave.
However, if he doesn't feel anything special, or even has some relaxed and beautiful feelings, then he hopes you have a peaceful belonging.
The tomb symbolizes a stable and peaceful life.
But one more thing, the dream is his own, so his dream, perhaps usually your image, is alluding to some of his own problems.