Yoga is the restraint of the modifications of the mind. Then the Seer is established in his own essential nature. Otherwise, there is self-identification with the mental modifications. The mental modifications are fivefold and are painful or pleasurable. These are correct cognition, misconception, fantasy, sleep and memory.
Correct cognition is based on direct perception, valid inference and verbal testimony.
Misconception is illusory knowledge based upon what is other than itself. Fantasy, empty of substance, is engendered by words and concepts. Sleep is the modification engendered by the abeyance and absence of mental contents. Memory is the not letting go of an object or image of subjective experience. This is indeed firmly grounded when it is persistently exercised for a long time, without interruption, and with earnest, reverential attention and devotion.