On this panel, the ecstatic behavior of a Dionysus festival is depicted. Dionysus is in the center—drunk with wine, naked, and "falling" backward. On the right of the image note the flute player, and the dancer with a hand drum. On the left note also the seated woman with a drum or cymbal.
Dionysus (= Roman Bacchus) was the god of wine, merriment, etc. and ecstatic rites were associated with the worship of him.
Dionysus was especially associated with the theater and thus depictions of him on panels on the stage area are to be expected.