Once establish in the SELF, one became a witness of what is experienced and also the person who is experiencing it.
Experience is only by the mind ,body complex ,it is experienced by the experiencer(enjoyer or sufferer). One who can further withdraw himself from the experiencer stage to a pure ,non perceiving state that is called self realisation.
This state is experienced by everyone but in limited quantity during deep sleep or sometime in your waking state during full devotion or surrender. One who established in this state or who can withdraw from this world at his will at any time is the perfect witness.