When you go to bed and close your eyes you should begin to drift off within 20 minutes or so. Passing rapidly through sleep stages 1, 2 and 3, you reach stage 4, deep sleep. Then comes REM (Rapid Eye Movement) sleep, when your eyes begin to flicker and you experience your most vivid dreams. After REM you begin to wake up a bit, before going back down into deep sleep. This cycle is repeated every 90 minutes or so throughout the night.
During deep sleep our brains work hard, moving memories from short-term into long-term storage, allowing us more short-term memory space for the next day. If you don’t get adequate deep sleep then these memories may be lost.
You might think: “I’ll cut back during the week then make up for it at the weekend.” Unfortunately, it doesn’t work like that, because memories need to be consolidated within 24 hours of being formed.
Since deep sleep is so important for consolidating memories, it’s a good idea if you are revising or taking an exam this summer to make sure you’re getting enough sleep. In one study, people who failed to do so did 40 per cent worse than their contemporaries.