Health experts at one of the world's leading institutions have shed light on how understanding one aspect of sleep can transform how you feel upon waking. Writing last year, scientists at Harvard Medical School in the US emphasised that, naturally, sleep is crucial for aiding the body to recover, repair itself and function optimally.

Moreover, they stated that comprehending sleep cycles could "help you improve your sleep hygiene and wake up feeling truly refreshed". They pointed out that most of us perceive sleep as simply not being awake.

However, they clarified it wasn't that simple, explaining that "scientists divide sleep into two major types: REM (rapid eye movement) sleep or dreaming sleep, and non-REM or quiet sleep. Surprisingly, they are as different from each other as each one is from waking - yet both may be important for energy".

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They explained: "Non-REM sleep involves three stages: light sleep, deeper sleep, and deep sleep. Sleep spe­cialists believe that the last stage, known as deep sleep or slow-wave sleep, is the main time when your body renews and repairs itself. This stage of sleep appears to be the one that plays the greatest role in energy, enhancing your ability to make ATP, the body's energy molecule.

"In deep sleep, blood flow is directed less toward your brain, which cools measurably. At the beginning of this stage, the pituitary gland releases a pulse of growth hormone that stimulates tissue growth and muscle repair. Researchers have also detected increased blood levels of substances that activate your immune system, raising the possibility that deep sleep helps prepare the body to defend itself against infection."

The experts noted that anyone whose deep sleep is disrupted will wake feeling far less refreshed than someone who's enjoyed proper deep sleep. When sleep-deprived individuals finally get some rest, they "will pass quickly through the lighter sleep stages into the deeper stages and spend a greater proportion of time there, suggesting that deep sleep fills an essential role in a person's optimal functioning".

They went on to say: "REM sleep helps restore your mind, perhaps in part by helping clear out irrelevant information. Studies of students' ability to solve a complex puzzle involving abstract shapes suggest that the brain processes information overnight. Students who got a good night's sleep after seeing the puzzle fared much better at solving it compared to those asked to solve the puzzle immediately."

Research from Harvard Medical School and other institutions has shown that REM sleep plays a crucial role in learning and memory retention. Participants tested on newly acquired skills demonstrated improved performance following a full night's rest.

However, when REM sleep was disrupted, these gains disappeared. Further details are available through Harvard Medical School's Special Health Report, Boosting Your Energy.