In Psychology, body and mind are related. The body affects the mind, and the mind affects the body. Motion and emotion are interconnected. The role of both can not be separated.
Do not believe? Try sitting, down, and folding your arms (like the posture of a sad person), and try to think of a happy and uplifting memory. Difficult is not it?
Now try to stand up, hands raised, and smile. After that, try to remember the sad things. Difficult is not it?
Such is the simple way to understand the connection between body and mind.
If you want to make your feelings happy, move your body and make your facial expressions as if you're happy;)
When you are feeling bad, complicated, or other bad feelings (badmood), it is easier to change those feelings or change your movement and posture?