Your mind and body do work together. If you relax your mind, it relaxes your body. It is sometimes impossible to get your mind to slow down and relax. If you want to test this theory further, simply spend a morning observing people at the grocery store. Notice how happy people tend to carry themselves differently than depressed or angry people.
Happy people tend to have their shoulders back and have an erect posture.
People who look unhappy tend to keep their heads down and their shoulder slouched. So if you want to feel less stressed, pretend you are not and you will be amazed how quickly your mind will start to respond to your body's actions.