The song 'I got a Feeling' by the Black Eyed Peas is one of the saddest songs I can thing of.
It's so overtly optimistic it feels to me that its making a point of being so. It's certainly how I tried and still try to be at times so as not to worry people or just try to pretend nothing is wrong. It makes me feel the desperation that this will be a good night or else.
It's become one of the songs of my life and it makes me cry (sometimes just almost cry) every time I hear it.
I Got a Feeling - YouTube
It is a great dancefloor filler but I don't know if it'll ever get me dancing. When I hear it, it zooms me back to the darkest days.