The Sound Of Music
Interestingly enough, it has been proven that people who like singing tend to be happier than those who don't. It doesn't even matter which kind of songs they like singing. As long as they like to sing, and frequently let their vocal chords strut their stuff, they statistically turn out happier people. Actually, it's not just singing. It's anything to do with music, be it singing, playing an instrument, or dancing to a tune.
Most likely, this is due to the fact that music is cathartic. Music captures the heart and emotions of the person creating the said music, and this catharsis is released to the surroundings. If the musician is feeling sad, the sadness is dispersed. If he feels happy, he declares it to the world, which, due to some reason not fully understood yet, makes him even happier. And when one sings the song again, plays the notes, or dances to the beat of it, they themselves take in the emotions locked in the song, relate to it, and release it for the same effect.
So sing more! Clear the dust of that old piano and strike a few bars! Let your body dance naturally to the beat of your favourite songs! If you're embarrassed to strut your stuff (or the lack of it), heck, do it when you're alone! The long term effects are way worth it. Music is one of the world's miracles that is often taken for granted. And if you can relate to a song, or an instrumental piece personally, all the better! As I posted a long way back, Positivity is not innate, it's a trained thing. And the catharsis of music can surely help you get there.
Maybe I should let my roommate go on his tone-deaf singing sprees more often. It's the effect that counts, anyway.