Sleepiness definition

It is clear, however, that melatonin has short-term mental effects. It definitely can cause drowsiness when taken during the day. Melatonin taken at night, however, will not cause daytime sleepiness. People who take melatonin are also less likely to respond correctly to visual and auditory signals. They are more likely to make mistakes and their reaction time decreases when they take this hormone. Several studies have shown that taking melatonin inhibits a person s ability to concentrate and can cause confusion. People should therefore not take it when they need to stay alert, such as when they will be driving a car. The effects begin within... 

For our purposes here we will define fetigue as a state of mind that a driver equates with sleepiness, tiredness, and lack of energy that is associated with some measure of decrease in performance or a physiological indicator of reduced arousal. It is significant that this definition dissociates fatigue fi om lack of sleep, though it is often correlated with it. Sleep and sleepiness - the tendency to fall asleep - are complex phenomena that depend on the interaction of many variables in addition to the lack of sleep (Johns, 2000 Ogilvie, 2001). 

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