Dr Murray Johns, chief scientist of Optalert says, ‘Drowsiness must be distinguished from fatigue. Some people think they are the same and use the word fatigue to mean drowsiness. This is misleading’.
Dr Johns defines drowsiness as the intermediate state between alert wakefulness and sleep. It is an unstable state which fluctuates between different levels. Drowsiness intermittently causes lack of awareness of the here-and-now; that is why it is so dangerous for drivers.
By contrast Dr Johns defines fatigue as a behavioural state associated with feelings of weariness and discomfort, muscle aches, and a disinclination to continue the task at hand. Fatigue gets progressively worse with the duration and intensity of the task. You don’t have to be fatigued to become drowsy, but you can be both fatigued and drowsy at the same time. Fatigue doesn’t fluctuate rapidly, over periods of a few seconds, as drowsiness does. Rest and inactivity relieves fatigue, but this makes drowsiness worse.
