The process of relaxation can be understood and achieved by the visual image, when you can visualize patterns of the body.
Visualize:
1. Your muscles are emanating brightness as they contract and are getting dimmed as they relax,
2. There is a glow in your each and every cell of the body,
3. There are flashes of light with the beating of the heart and so also with the other organs while they work.
4. The waves of energy is shifting between the brain and the spinal chord.
5. Each sense organ and particularly eyes and ears is sending a beam of light to the brain.
6. Each time brains receive information, from any part; light sparkles and also each time sequentially light sparkles as the brain processes bits of information, makes decisions and sends instructions back to the various parts of the body.
7. You can see the brain cells, the neurons, while the brain is working.
Sleep and Meditation. During sleep, the body is relaxed but is dim. The internal systems and the senses get slowed and their connection with the brain. Brain is active but patterns are different. The energy is now in the brain and spinal chord.
In meditation, the body is more relaxed more than in sleep. All organs are working and glowing but senses are shut down.
Energy levels are centered in the frontal brain and spine. This energy is sometimes withdrawn by certain Hatha Yogis to the level of stopping the heart and the autonomic nervous system, which is not the purpose here. Most people can concentrate their energy to energize their divine eye, to the level of self realization. They can get their divine eye activated through the Guru.
So the First step is physical relaxation: This is eliminating stress and tension from different body parts. Then there is deep relaxation through controlling energy levels.
The Second step is mental relaxation: This requires greater control and is difficult. As the mind is wandering, with mental relaxation you can see thought by thought passing. This is controlled through concentration and focusing on breath.
The "Energy, Body And Mind" equation: There is a strong correlation between the three. If you alter one, the other 2 too are altered. If you relax one, tense or excite one, the others too are likewise changed. For e.g., when you face sudden danger, your mind gets excited, breath too gets excited and muscles too get excited getting energy and are ready for action. So the Mind- Body-Energy cycles are inter-related.
The breath is most visibly felt and hence easiest of these three to control. So by controlling the breath, you can control your mind and energy.