Tamas guna dominance due to darkness is believed to be the natural status of night (Ratri). And due to dominance of tamas sleep is induced. This is the course of natural cycle of sleep. Thus sleep that is induced due to day and night cycle, at night, is included in this category. | Tamas guna dominance due to darkness is believed to be the natural status of night (Ratri). And due to dominance of tamas sleep is induced. This is the course of natural cycle of sleep. Thus sleep that is induced due to day and night cycle, at night, is included in this category. |