Think about some of the movies you've seen. “Jaws” wouldn't be the same without its daunting, low, repetitive sounds that makes you sit on the edge of your seat waiting for the shark to attack from somewhere. Then there's “Titanic” and its gorgeous love theme that permeates throughout the movie and throughout ourselves with its bittersweetness, generating the beauty of love and the tragedy of the massive ship's sinking and loss of so many lives.
One aspect of “healing” music is to stir our feelings, to help us deal with grief, sadness, anger or other feelings. By allowing ourselves to FEEL those feelings, the intensity will eventually lessen and even dissipate, resulting in being healing for us. When we avoid our feelings (consciously or subconsciously) they nonetheless tend to build up inside. They don't just go away. Music can be a tool to help us deal with feelings within us, whether we're aware of them or not. This is one of the wonderful ways music can be incredibly healing.
