And sometimes they are the vehicle with which I can bleed off some of the emotion that collects during the darker times. I don't know if that makes any sense.
When I am feeling really down, sometimes I will play music to draw that out of me - force a physical reaction to what I am trying to contain. Gets it out of my system, or at least I think that's what it does.
Then when things pass, and I feel more even-keeled, I gravitate towards different music. More energetic is probably the best way to describe the difference.
It is all completely unconscious, and seems to happen naturally. I guess as long as it means I won't completely lose my mind, I can live with it.
Peace!