Mental visualization is an important part of yoga nidra practice. Its purpose is to stimulate the subconscious and unconscious levels of the mind. This helps to evaporate suppressed feelings and memories, and thereby clean the mind of tensions. At a deeper level, the use of specific symbols can induce perception of the unconscious layers of the mind, those aspects of your being that are currently hidden and unknown to you. Inner visualization helps to awaken your inner potential and bring knowledge.
All of us have this ability to visualize. In fact, we do it every night when we dream. Dreams are pictorial expressions of the subconscious mind, and sometimes the unconscious mind. They take the form of symbols and stories and they all have significance. Most of them arise merely to release pent-up inner tensions and conflicts; others may have universal significance and symbolize a truth of existence.
In yoga nidra we attempt to induce dreaming, but dreaming with two main differences:
1. The dreams are controlled, selected and guided. Ordinary dreams are completely random.
2. The dreams are experienced consciously. Most ordinary dreams in sleep are unconscious.
In yoga nidra, the selected, conscious dreams are induced by visualization in accordance with the instructions of the teacher.
The teacher should choose the symbols or objects of visualization very carefully. They should be chosen so that they help to remove tensions from the mind of the practitioner by stirring up old memories. In some cases this mental stirring up with symbols may cause some initial emotional upset, perhaps as one relives a past, long forgotten painful event. Once this initial emotional shock is experienced, the tension is exhausted and there is greater harmony in the mind. Sometimes the symbol that causes the release of pent-up tension can seem to be insignificant to another person. Let us give an illustration.
A lady was doing yoga nidra. Her teacher told her to visualize a red car. There was an explosion in her mind. Immediately she started shaking with emotional shock, but after a short time she felt very relaxed. Later she explained to her teacher what had happened. She had been in Nazi Germany. When she was very young her father and mother had been taken away by the Gestapo in a bright red car. She never saw her parents again. From that age onwards she forgot (or rather suppressed) the memory of the incident. Yet, in seed form, the emotionally loaded memory had remained firmly impressed on her mind. It caused her endless unhappiness in life, though she did not know it. All she knew was the unhappiness that it caused. The mere mention of the words red car while she was in the perceptive state of yoga nidra induced remembrance. She actually relived the past, the time when her parents were being taken away from her. She felt and expressed the emotional shock during yoga nidra. After a short time the emotional contents of the memory were exhausted. She felt very relaxed. This was the start, only the start mind you, towards a happier life.
This is one example of the mechanism of releasing deeper tensions of the mind in yoga nidra through visualization. All the tensions of the mind, minor or major, can be removed in a similar manner, though generally their manifestation will not be as obvious as the example that we have just given. Most tensions evaporate more smoothly.
When most of the tensions have been removed from the mind, then it should be possible to hold one image in the mind. This is called dharana where one visualizes one symbol to the exclusion of all others. This is a more advanced stage of yoga nidra and leads to dhyana.