1. A method for analyzing drowsiness of a subject having a head and an eye, the method comprising: a. measuring motion of the head of the subject in at least one dimension; b. measuring motion of the eye of the subject; c. deriving at least one physiological indicator of drowsiness in a waking subject, the at least one physiological indicator, selected from the group of saccade frequency, saccade speed, blink duration, blink frequency, instrument-world scanning performance, and gain of vestibular-ocular reflex, based on motion of the head and the eye; and d. comparing the at least one derived physiological indicator of the subject with predetermined ranges of acceptable values in such a manner as to determine an onset of drowsiness in the subject.