The most common posture adopted for doing meditation is sitting holding chest, neck and head tight in a straight line.
As suggested by Swami Vivekananda in Raja Yoga:
But the main part of the activity will lie along the spinal column, so that the one thing necessary for the posture is to hold the spinal column free, sitting erect, holding the three parts — the chest, neck, and head — in a straight line. Let the whole weight of the body be supported by the ribs, and then you have an easy natural postures with the spine straight. You will easily see that you cannot think very high thoughts with the chest in.
We can also find it in Shvetashvatara Upanishad:
II-8: Placing the body in a straight posture, holding the chest, throat and head erect, and drawing the senses and the mind into the heart, the knowing one should cross over all the fearful currents by means of the raft of Brahman.
So, after sitting in recommended posture, there are many different methods and tricks for meditation suggested by different Yogis but more or less the goal is to reduce the number of thoughts coming in mind to make achieve the state of no manual thought eventually. Now, getting closer to this state can result in either of two state 1) Deep sleep 2) Dhyana (not going into deep in the various stages of Dhyana).
So, as soon as the mind starts to become thoughtless the state similar to sleep is felt sometimes.
- At this moment, how can one know or verify that the state I'm going is deep sleep or Dhyana?
- Returning from such state after remaining the same for several minutes, how can one know/verify that the state I was in was deep sleep or Dhyana?
Is there any tip suggested in scriptures or work of Yogis or disclosed by any well known Yogi?