Perhaps the key is non-attachment.
There are ups and downs, highs and lows, but they all come and go. Impermanence is the only permanent trait of it all.
If that's the case, then the only thing to do is live in the present moment and deal with what's going on right now. If you are happy, enjoy the crap out of it. Revel in happiness, have fun with happiness and above all, immerse yourself in the happiness. It will soon pass, so enjoy it while you can.
Same goes for unhappiness as well, while it is around, do the best you can with it. You don't have to enjoy it, but you can improve your outlook around it. Also remember that it too will pass, at it will lighten the burden and heaviness of it all.