The following is a summary of Bhagavan Sri Ramana Maharshi’s teaching on the Self.
Self-Realization cannot be described because Self can never be an object of perception. The Self is always the subject. The Ultimate Subject. When the mind is temporarily absorbed in the Heart, the Self is known with immediacy as the eternal presence. That is called Kevala Nirvikalpa Samadhi.
However, even after having attained Nirvikalpa Samadhi, the mind has the tendency to sprout up again with its conditioned habits due to the force of karma (previous tendencies). Hence the need for awareness and practice of reflective inquiry continues.
When the mind is completely resolved in the Heart, the Self naturally and spontaneously dominates in all states of consciousness (waking, sleeping, super-conscious). That is known as Sahaj Samadhi or the natural state. In this state, the karma that has started to bear fruition will continue until the end of the body. The former conditioning might still manifest in the sage but loses its fundamental hold to create new karmic forces for the future.
Sri Ramana describes Self-Realization below.
“The state we call realisation is simply being oneself, not knowing anything or becoming anything. If one has realised, he is that which alone is, and which alone has always been. He cannot describe that state. He can only be That. Of course we loosely talk of Self-Realisation for want of a better term.”