After I had visited Swami Muktananda in 1981, I came back to Australia with a peculiar sensitivity to music. I obtained a job, and at lunchtime I would drive to a quiet spot, eat my lunch, then turn on the radio, tuned to a classical music station, and go into a light trance.
I would sit with a straight back, and feel the music "going into" the point between the eyebrows, or Ajna chakra. By also consciously suggesting that the consciousness should ascend the spine, it did, and the boundary of my body became inside the head only. I felt a delicious peacefulness.
Our consciousness flows into the body in the normal waking state, and we feel our personal boundaries to be the tips of the toes, fingers, and top of the head. Beyond that we consider to be "outside" the body. I discovered that the boundary is variable (in both directions). Certain schools of kundalini and kriya yogas aim to contract that boundary, by consciously withdrawing the flow of consciousness up the central column of the spine (sushumna).
When my consciouness-boundary was within the head, the rest of my body felt "external". A phase beyond that is that body-awareness is totally lost, yet the person remains aware -- the practitioner is thus intensely focussed within a boundary close to the "source" of consciousness, or Self. This is samadhi as described by the classical yoga books, in which bliss and boundlessness are experienced, but there is no physical awareness.
When the practitioner comes back to physical awareness, the samadhi is gone. Yogis claim however that repeated practice will gradually bring Self awareness regardless of where the consciousness flows or how many thoughts occupy the mind.
.... discussion on Advaitism follows this, has a very different perspective. Read here