Nirvikalpa samadhi is recognized as one of the highest states of samadhi. The state of consciousness before this is savikalpa samadhi where the experience of time and space alters. The yogi recognizes that everything is complete and there is nothing more to do. Thoughts still exist, but they do not affect the yogi in this state. After experiencing savikalpa samadhi, however, normal human consciousness returns.
The difference between this stage is that in nirvikalpa samadhi all thoughts dissolve. This is considered a state of being at one with the Divine. It is a state of true ecstasy, oneness and limitless bliss. After experiencing nirvikalpa samadhi, a yogi does not wish to return to the world. They may forget their own name, how to speak or how to think properly. With practice, though, they may find it easier to experience this state and then function in a normal way afterward.
Beyond nirvikalpa samadhi is sahaja samadhi. This state is only achieved by very few spiritual masters and is said to allow them to achieve the highest level of spiritual consciousness while still functioning in the physical world.