Sleep inertia is a physiological state characterise by a decline in motor dexterity and a subjective feeling of grogginess, immediately following an abrupt awakening. Sleep inertia can also refer to the tendency of a person to want to return to sleeping, even after suitable rest has been achieved. Typically, sleep inertia lasts up to 3 hours for a night wake up and up to 90 minutes for a day wake up. If the subject is awakened due to a perceived danger, however, the duration of sleep inertia is reduced to only a few seconds.