Many people think of sleep as 'switching off.' In fact, your brain is very busy while you sleep — and the work it does at night decides how well you live during the day.
When you sleep, your brain sorts through everything that happened while you were awake. It moves important information into long-term memory and clears away things you do not need. Scientists have found that the brain even washes itself at night, using a special liquid to carry away waste. This may be one reason why a tired brain loses its concentration: the cleaning is not finished.
Sleep also repairs the body. While you rest, your muscles rebuild, your skin heals, and your body builds its defense against infection. People who sleep too little catch colds more often, and they feel hungrier during the day, because short sleep changes the body's chemical signals about food.
How much sleep do you need? Most adults need seven to nine hours, teenagers need about eight to ten, and small children need even more than that. Some people say they can live well on five hours, but tests in sleep laboratories show that almost nobody really can. Tired people simply stop noticing how tired they are.
The good news is that better sleep is a skill you can learn. Go to bed and get up at the same time every day, even on weekends. Keep your bedroom dark, quiet, and at a cool, comfortable temperature. Stop drinking coffee after lunch, and put your phone away before bed — the bright screen tells your brain that it is still daytime.
One more tip from sleep science, and it is a nice one for language learners: review your new words before you sleep. While you sleep deeply, your brain quietly practices them for you — for free.