Paradox: My Cup Overflows

Are Christians always grumpy? Or do we have to be bubbly rainbow unicorns all the time? Should we expect some happiness in this life, or should we just wait until heaven? And what's the difference between joy and happiness anyway - or is there a difference? If you're like me, my happiness levels seem to fluctuate minute to minute, but I'm convinced that Paul had a vision for something more profound and stable than I tend to be.