Nirvikalpa Samadhi is the highest state of Meditation.
It is a state of Self-realization or God-union while the yogi is in his 'normal' waking state.
In the initial states of meditation the yogi enters a very deep state of trance in which his or her body is in a state of conscious death. Although the body may appear lifeless and cold to the touch tremendous expansion of consciousness is experienced. The yogi begins to experience life for the first time!!! He begins to learn how to live his life more fruitfully and effectively!
Eventually, when deeper states of meditation are achieved through persistent meditation and refinement of consciousness the yogi learns how to become irrevocably established in deep meditation or samadhi without bodily fixation and in his normal waking state.
Nirvikalpa Samadhi begins with the dawn of Cosmic Consciousness.