You are certainly not expected to feel giddy and joyful after such a loss. It is a mitzva to be proactive in trying to find ways to make yourself feel better. Yom Tov isn’t about faking happiness. It’s about making yourself happy. So if you know that crying is therapeutic, then cry (for the halachic basis for this – Rema OC 288, see Aruch Hashulchan). Read a book about dealing with loss. Drink some wine. Spend time with people who make you feel good. Again, there is no mitzva to put on a fake smile. Just to try to make yourself feel better. And while this is only an explicit mitzva on Yom Tov, it is a worthy attitude all year round.
