Without wishing to be censored, or controversial, music is the only thing I know - aside from orgasm - that sends shivers throughout my entire body. No other art that I know can affect the emotions, or move me, in the same way. I love film - overall probably more - but something happens when you get to know a beautiful piece of music really well that does not happen with other art.
With books, the rule is that you read it a second or third time and the impact lessens. With music, the reverse is more true - listen a second, third, fourth, fifth, hundreth, thousanth time....... With a good piece of music, it takes hundreds if not thousands of plays before the emotional impact of listening starts to wear off.
I can fully understand why it is an effective therapeutic tool - it engages the senses more fully and completely, and for more time, than any other art.
Best wishes
Rory