The need for sleep varies among people - sleeping eight hours per 24-hour period is common, and seven to nine hours is needed to optimise performance. Sleeping less than 4 consolidated hours per night impairs performance on vigilance tasks. Acute sleep loss, even the loss of one night of sleep, results in extreme sleepiness.
The effects of sleep loss are cumulative. Regularly losing one to two hours of sleep a night can create a ’sleep debt’ and lead to chronic sleepiness over time. Only sleep can reduce sleep debt. Sleep loss can be work-related or a lifestyle choice.
The quality of sleep is also important. Sleep disruption and fragmentation lead to inadequate sleep and can negatively affect functioning. Sleep fragmentation can be caused by illness, including untreated sleep disorders.
Disturbances such as noise, young babies, children, activity and lights, a restless/snoring spouse, or jobrelated duties (e.g. workers who are on call) can interrupt and reduce the quality and quantity of sleep.
A combination of these factors increases crash risk substantially.
Sleepiness leads to accidents because it impairs human performances that are critical to safe driving.
People can use physical activity and dietary stimulants to cope with sleep loss and mask their level of sleepiness. However, when they sit still to perform repetitive tasks like driving, sleep comes quickly.
Sleepiness leads to:
The Epworth Sleepiness Scale (ESS) is an eight-item, self-report measure that quantifies individuals’ sleepiness by their tendency to fall asleep ’in your usual way of life in recent times’ in situations like sitting and reading, watching TV, and sitting in a car that is stopped for traffic.
People with a score between 10 to14 are considered moderately sleepy, whereas a score of 15 or greater indicates severe sleepiness.
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