i'd say grab some simple nostalgia games from your childhood, i know one of the first things i do if i'm in a funk is fire up the nes and play mario 3, bubble bobble, or any other games that bring back good memories.
anything thats easy, familier and doesn't require much thought, even better if you invite a buddy over and order a pizza or something
I actually find that nostalgia does the exact opposite. Knowing that my life used to be awesome and that now it sucks actually makes things worse. >_>
Man I agree with you 100%, nostalgia makes me feel like i'm in a bad mood cause all I ever do is think back to the old days, and I miss them.