Gratitude and sympathetic joy

It's always good to remember the importance of gratitude. This quote by Steven Levine also refers to mudita - or "sympathetic joy":

Gratitude is the state of mind of thankfulness. As it is cultivated, we experience an increase in our "sympathetic joy," our happiness at another's happiness. Just as in the cultivation of compassion, we may feel the pain of others, so we may begin to feel their joy as well. And it doesn't stop there.

— Stephen Levine in A Year to Live

Whenever you're out of sorts, remember gratitude. Make the effort to call to mind something for which you are thankful. Start with your five senses. Be grateful you can see, hear, etc. That will get you started. Then other awarenesses are sure to follow.