Regular practice of yoga slows down the action of the sympathetic nervous system. This means the release of stress hormones is controlled. It improves the functioning of the parasympathetic nervous system, which controls your ability to relax.
One must learn the art of relaxation. Relaxing all the muscles of the body from head to feet will bring rest to body and mind. Holding tension in any part of the body means dissipation of energy. So, one must practise relaxation.
Take a few deep breaths and lie flat on your back. Relax the muscles of the body. Roll from one side to another. One can relax each part of the body separately. In addition, one must have a mental picture of calmness and strength.