CNN: A well-rested person does not fall asleep immediately, says sleep specialist Rebecca Robbins, an instructor in the division of sleep medicine for Harvard Medical School.

“Falling asleep does take about 15 minutes for the healthy sleeper,” Robbins added. “Falling asleep is distinct from sleep itself, which can be frustrating when one is extremely tired.

“Nevertheless, be patient that sleep will come and the more you stress about not being asleep, the lower your chances of falling asleep,” she said.

Robbins, who coauthored the book “Sleep for Success!,” equates it to having been deprived of food. “If you are starved for food, you will devour your next meal immediately, whereas a well-nourished person might not be as ravenous and in dire need of nutrition immediately,” she said.

Adults need to sleep at least seven hours a night, while school-age kids need nine to 12 hours and teens need eight to 10 hours each night, according to the US Centers on Disease Control and Prevention.

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