Hear me out for a moment.
I really like bananas... I buy a couple bunches and they're gone in a few days. Yummy. But then I don't get to the store for a while, and so on. One day not too long ago, I saw a bit of a correlation between my mood and the days I had bananas.
Digging around a bit, bananas (or papaya or dates) turn out to be one of the fruits that increase serotonin levels, one of the chemicals that might play a role in depression.
So... at this point it might be all placebo, but I don't care. I eat bananas every day and feel generally good! (Hey, it's only a couple bucks to try out, and at least it's not heroin or something!)
Naturally, the banana is no substitute for professional help, etc.