 Experimental subjects who suffered increased fatigue in a rotating environment apparently recovered from this side effect when the same environment ceased motion.In similar studies, control subjects lacking vestibular function did not experience the motion-induced drowsiness associated with the sopite syndrome, while subjects with normal-functioning vestibular systems did experience increased fatigue in the rotating environments.The relation of the visual-vestibular stimulus to the sopite syndrome may be observed when comparing airline cockpit crew with cabin crew.