why does music make me cry?

So I was talking to Tommy about music and I decided to tell him to check out Imogen Heap. She is a great singer, I know about her music because of dance, she sings very popular music for people to use for lyrical dances (see video bellow). Then I started to listen to some of her music because I hadn't in awhile. Her lyrics are wonderful, and the beat is simple yet compelling. I find my mind totally absorbed in the song. I stand and start making up a lyrical dance to her music. And it fills my mind with playful joy, yet I can't help but be a little saddened. It is somewhat depressing, the lyrics a bit, but mostly the way she uses the rhythm and beat.
Well I sound like a writer now :]