The four types of samadhi that we discussed are vitarkânugama samâdhi (the calmness that you get from special logic), vichârânugama samâdhi (equanimous state where you are aware of the thoughts, yet they are not disturbing you), anandnugama samadhi (blissful state) and asmitânugama samadhi (deep experience of meditation with just the awareness that 'you are'). All the four are called sampragnâtha.
Now, how to achieve these states of samadhi? The next Patanjali Yoga Sutra says it is very simple.
Viramapratyabhyasapurvaha samskara sheshonyaha
The practice of deep rest consciously happens (naturally) in some people due to old impressions. Just by doing something, you cannot achieve this awareness. You cannot bring up the intelligence or alertness in you by effort. This happens without effort, by relaxation, by reposing in the Self.
- Patanjali Yoga Sutra #18
Unconscious rest is sleep, which we are forced by nature. You are not resting; you are forced to rest. You are so tired and nature is pulling you down and forcing you and making you rest. Real rest happens only in deep meditation because you are consciously resting. You allow yourself to rest. Do you see the difference? Sleep is putting you to rest but meditation is you resting on your own. This is abhyasa (practice) of deep rest consciously.
Some people have to practice this in order to be equanimous and bring up more awareness in them. For some people it is by old impressions (samskaras) of past lives, births; it just happens. Sometimes right from the birth or sometimes at some particular period in life, they start opening up. This is samskara sheshonya. Have you noticed this? Some people, after 30-40 years, suddenly open up to some spiritual experience. They have more awareness. But unfortunately, most of those people get misguided. This is because there is no root of understanding of yoga. At that stage instead of getting misled by evangelic experiences, they should know that they are all from samskara shesha (old impressions). It is a different type of samadhi.