Dhyana is seventh limb of real (patanjali) yoga. Dhyana is a Sanskrit word,it means meditation.
Dhyana is a meditation not concentration.In yoga meditation and concentration is considered very differently, both are well directed thought process but they differ in the purpose and mood with which they are undertaken. Concentration is the process of determining a particular object out of many,dhyana is the maintenance of the same object to the exclusive of other vibrations for a considerable length of time. Concentration is channelized in one direction but gives rise to multiplication and chain reactions of thoughts, whereas in dhyana, concentration on an object is only starting points of process. Eventually the object ceases to have meaning in the context to the whole experience.
Eventually dhayan becomes more passive, gradually eliminating thoughts. Dhyana is training in increased, yet controlled, introversion through a gradual diminishing and final elimination of the impact of all external stimuli .It is a result of a change in outlook. In dhayna thoughts are not focused on greed, amibition or overtaken by curiosity. The basic principle of dhyana is the development of internal awareness for which there are innumerable means. The human mind has two directions, external and internal; our thoughts are usually directed outwards and much less frequently inward. And this is because we have to constantly concerned with the external world.so gradually we develop habit of directing our thoughts outwards, and sooner or later, of constantly and restlessly thinking about it. We are so lost in,so confused by,external that we forget who we are and what we really want. Meditation helps us to communicate inner peace/voice.
An uninterrupted process of meditative requires minimum or no disturbance from the external or internal environments. That is only in the absence of the sensory inputs and their perception; one would be able to concentrate his mind for meditation .The main purpose of the meditation asanas is allowed the practioner to sit for extended periods of time without moving the body and without discomfort. Deep meditation requires the spinal column to be straight and very few asanas can satisfy this condition. Furthur more in high stages of meditation the practitioner loses control over the muscles of the body.
The meditation asanas, therefore helps to hold the body in a steady position without conscious effort. Your lazy will think: why not to lie down in shavasan then for meditation since it satisfies all requirement?,because in shavasana there is tendancy to drift into sleep. For meditation it is essential to remain awake and alert while going through the various stages which lead to successful meditation. There are four asanas which are useful for meditation ;padmasanas,ardha padmasana,siddhasan,samsana,sukhasana,swatikasna,vajrasana.initially most people find it difficult to sit in one asanas for a long time,so beginers should start with ardha titali,shroni chakra,poorna titali,vayu nishkasana,kawa chalasana udarakasana,shithalyasana. These meditative asanas provides good base for the body, keep your spine erect , straight spine prevents compression in an abdominal organs, leaves the abdominal muscles free for the breathing activity. Meditative asanas facilitates abdominal breathing, it is also noticed that energy requirement in meditative asanas is less, Required force to return deoxygenated blood is less,so easy venous return. Thus it is advisable to sit in above mentioned meditative asanas for meditation.
Benefits of dhyana includes positive thinking,inner peace,improvement in concentration,fall in heart rate,blood pressure,oxygen requirement and an increase in alpha wave brain rhythm activity. Dhyana also helps to reduce (stress related) total cholesterol levels.
Method of dhyana (meditation)
1) Find some time out of your daily schedule,Find a quiet place and sit down ,Be comfortable. Relax.
2) Take one of the mentioned meditative asanas , Keep the face serene. Chin up , Close your eyes slowly to experience a void darkness. ( Remember to keep your eyelids closed throughout the following steps)
3)Look into your eyelids as if seeing with your eyelids open.
4) Keep your mind empty of people, place, things, color or any form.
5) Try and concentrate on the inner side of your forehead , Thoughts may arise, but do not make chain of thoughts, bypass them and keep looking with your eyelids closed, going deeper and deeper, leaving form, name, color, and activities far behind you. Again thoughts may arise again do not make chain thoughts,e.g.say first thought is I will go to meet girlfriend,now second thought is I will hug her.so if first thought of meeting girlfriend arise, then second chain of hugging her , you have to miss.
6) Experience the state of thoughtless, try to enjoy breathing, and try to feel coolness around your nostrils. 7) As you go deeper and deeper with your eyes closed in this dark place, you may see the swirling of smoke-like colours flickering in the darkness and silvery flashes of light.
8)Look straight in front with your eyelids closed and keep going further and further.
9) To keep you alert in meditation, take slow deep breaths.
10) Keep breathing steady. Let thoughts come and go. You're on a journey going beyond the body and form.
11) After you feel totally calm and relaxed, gradually open your eyes and spring back to life with renewed energy.
12) Practice this meditation daily for 20 mins.