Holding on to reality is Samadhi.
Holding to Samadhi with effort is savikalpa Samadhi.
Merging in reality and remaining unaware of the world is nirvikalpa Samadhi.
Merging uncousciously and remaining unaware of the world is sleep.
Remaining in the primal,pure,natural state without effort is Sahaja nirvikalpa Samadhi.—Maharishi Ramana.