My garden is my own little piece of Heaven. I love to sing songs while I am planting, digging, pulling weeds, or just admiring.
I tell my adult children, and husband that when someone is singing, you can bet they are happy. Maybe it is the singing that makes them happy too. I like to think that it is a big uncontrollable circle.
So if you are sad, sing a silly song. The sillier, the better. It will make you happy. Then because you are happy, you will sing more. Then others will hear you sing; they assume that you are happy, and they might be missing out on something. Then they will sing too, and then THEY will be happy.
If you are happy and you know it–sing a song:)
If you are not, sing anyway.