Very few people can meditate. What most people experience when they sit for meditation are the activities of the subconscious and unconscious mind. The mind works on four levels: conscious, subconscious, unconscious and super-conscious. Meditation occurs when one makes contact with the super-conscious. But to do this, one has to get through the subconscious and unconscious.
The subconscious mind acts as a censor for the untold millions of pieces of information which are fed to the brain by the senses every second. Very often the sub-conscious suppresses information which would cause the conscious mind stress or strain. These suppressed impressions are buried in the unconscious mind where they can, and often do, create many psychological blocks. A young child, for example, sees a nasty accident, and the subconscious mind buries the nastiness in his unconscious. But from then on the child has a horror of blood, without remembering why. In this way many psychological problems are created.
To reach the meditative state one has to find the way through these deeply hidden road blocks to the super-conscious. This is why some people have unpleasant experiences during deep relaxation and pre-meditative practices. When the conscious and subconscious minds are relaxed, the unconscious is not suppressed, and all the buried unpleasantness comes up to the conscious level. Very often this takes the form of horrible visions, monsters, strange auditory effects, or other disturbances. These should be welcomed, not feared. Remember that they come from within, and can do no harm. On the other hand, many people have pleasant experiences during this process.
Meditation occurs when the barriers of the conscious, subconscious and unconscious minds have been passed, and the super-conscious. mind is reached. Asanas and pranayamas are therefore as important as meditation itself. They are the keys by which the doors of the energy store are opened, and thus they are named the conductors of prana.