Think about the last thing that brought you joy. After the 30 seconds of joy that memory brings, decide that the happiness it provided is worth the effort to either recreate the same event or a comparable one. If it involved other people, call them and be honest.
“I’ve been really down for a while, and I was thinking about how awesome [fun thing] was, and wondered if you would be up for a trip down nostalgia lane?”
See it through. Don’t set the bar of expectations too high, as it’s easy to let nostalgia over-amplify how awesome something was.
During the recreation, focus on the moment, not what it was like “the last time”. Let yourself have a good time. Turn your filter off and be real and genuine with people, as long as it doesn’t involve hurting their feelings (if you don’t like someone, don’t invite them). Realize afterwards that part of the fun is being yourself with people who care enough to show up in your time of need.
Many of us walk around without “recent joy” in our lives. Happy and Sad are not black and white concepts. There are degrees of these emotions, and sometimes you overlook the joy in smaller things. For me, a great cup of coffee with a moment of peace to think about weird ideas is a great sense of joy.