Insta-therapy songs

You know the ones I mean: you know the songs forwards and backwards and you've loved them forever. They instantly take you to your happy place, despite the shitty circumstances you're in.

I was lucky enough to have it happen twice yesterday - both times in the car. Like many of us, I'm freaking out about money. I've been a stress case, and not very fun company at holiday gatherings (although I try). Also, 2008 blew. But I heard The Shins' "Know Your Onion" and Pixies' "Where is My Mind?" yesterday and each time, as soon as the opening guitar kicked in, all was right with the world. By the time the song was over, I was singing at the top of my lungs and could barely remember what had me so upset.

How the hell does that work, even after I've heard the songs a thousand times? What is it about these songs that does it - when plenty of other great songs probably wouldn't have cut it yesterday? And what songs do it for you?