Um, yeah. You don’t “cheer up” depressed people. It just makes it worse. The thing to do is just be there for them, sit quietly with them if they wish, and just listen without offering advice.
As I recall, Willard J. Farnsworth “Spook” Spookingdorf III is actually Id’s father and the rightful king, who is in the dungeon for calling the King a fink.
Bets’ problem is not uncommon. It is called the letdown effect, known as “post event letdown” or PELD. After completing a big project or task, one loses a sense of purpose, becoming sad and irritable. You have gone from being THE person to someone with nothing to do. You no longer have the same mental stimulation. People have even committed suicide, just when you think they should be thrilled with their achievement. The dopamine release, and flooding of endorphins and serotonin leave you riding high while the event happens, and then, suddenly, nothing. There are many ways of dealing with this, with sharing your feelings being one of the big ones. It is also good to reflect on things that make you happy, get some exercise, and look forward to the next big event.
Just be sincere. Once you can fake that, you can do anything.