Further to http://vedanta.manishverma.site/you-are-not-your-body-a-talk/, http://vedanta.manishverma.site/are-you-the-body/, http://facebook.com/VedantaManishVerma/posts/557381750947813, http://facebook.com/VedantaManishVerma/posts/204139029731685 and considering the fact that one does not know where one was during the sleep or under the influence of general anesthesia, the question arises that if a being is not the body-mind then who is he/she/it? Let us call the inner nature of being as inner-self for the moment.
Generally, a person identifies himself/herself with body-mind and is not aware of the presence of the source. In some moments one can experience a silent presence if one pays attention. In such moments the inner-self becomes aware of itself.
Meditation (ध्यान/dhyan) is the experience of the inner-self. It is a state where one does not identify with the body-mind and experiences the inner-self. In this state one can observe the activities of the body-mind without getting attached to the thoughts. Since most of the human suffering is due to the attachment with the thoughts, it ends when this attachment ceases. In deep state of meditation, one identifies with the inner-self itself (which means witnessing body-mind as a separate entity) and eventually there is a sense of oneness with everything which is called Samadhi. Samadhi is like deep sleep with full awareness. In the highest state of Samadhi, the individual being identifies with the universal field or experiences expanded-self.