I agree dancing helps a lot because: Emotion comes from Motion
So you create constructive emotions by dancing it also opens the diaphragme
( respiratory system ) this gives a better posture and good posture has a lot to do with confidence. We should always pay attention to our posture.
There is another way you can open the diaphragme but I dont suggest it.
Its by eating more then necessary or by going shopping.
This is what people usually do wen they feel down.