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The longer you go without sleep, the more extreme the consequences. The brain hallucinates, sees shadows and hears sounds that aren't there. Individual sleep requirements are largely determined by heredity. There are people who can manage with five hours sleep, while others need ten hours to feel well rested.

Sleep researchers have found that people in western countries sleep one hour less on average than they did 20 years ago. They were also able to show that people who don't sleep enough perform less well during the day – and often don't notice it. This is because it's possible to become accustomed to getting too little sleep. This can trigger a paradoxical phenomenon: the more people work, the less they sleep. Scientists at the Bundesanstalt für Arbeitsschutz und Arbeitsmedizin [Federal Institute of Occupational Safety and Health] have found that the longer our working hours, the more likely we are to suffer sleep disorders. However, you can only perform properly if you are well rested.

Seven hours of sleep

Many studies have shown that most people need seven to eight hours of sleep. The rule of thumb is that if you can concentrate on your work during the day without feeling sleepy, even if you have to spend lengthy periods sitting down, you have found the amount of sleep you need.

Finding out how much sleep you need

The holidays are a good opportunity to find out how much sleep you require. Go to bed at the same time each evening without setting your alarm clock. Don't get up until you feel awake and properly rested. Then make a note of how long you slept in the night. This will tell you how much sleep you need – and you should also make sure you get this amount of sleep during the working week.

It's possible to catch up on missing sleep

Sometimes you simply can't sleep. However, fortunately it's possible to catch up on sleep. This has been proven in a study by American sleep researcher David F. Dinges from the University of Pennsylvania in Philadelphia and his colleagues. If you sleep in after a couple of short nights, this will give you a lot of your strength back. However, you will not be really fit until you have slept properly for several nights.