Hatha Yoga refers to a state of consciousness where the sense of separation between subject and object dissolves, and all one is left with is the sense of oneness. This expanded feeling produces a euphoric state where thought, time and space no longer exist.
Classical yoga, as defined by Patanjali in his Yoga Sutras, is that state achieved where fluctuations of the mind stop – “Yoga Chitta Vritti Nirodhah”. By first concentrating the mind on a single object over an extended period of time as is done in meditation, eventually the mind through an act of grace can stop entirely. Once stopped, a tremendous energy springs forth as a natural consequence, and one enters into a state called samadhi.