World Sleep Day

World Sleep Day falls on March 21

Our bodies sleep in 90-minute cycles. It means if we sleep 8 hours a night, we will experience five to six cycles each night. At first, you enter a light stage of sleep when your muscles relax. The body temperature drops and the heart rate(心率) slows. Next comes deep sleep. It's difficult to wake up during this stage. This is when your body repairs itself and builds up energy for the day. At this time, your heart rate is at the lowest point. Finally, you get into the rapid eye movement(REM) sleep stage. It is when most dreaming happens and the heart rate rises. After the REM sleep stage, the cycle restarts.

Waking up in the“wrong” stage can leave you feeling especially tired. So it's important to wake up at the right time. And you shouldn't just start your sleep cycle whenever you want. Many young people go to bed late and get up late. They think as long as they have 8 hours of sleep, everything will be fine. But in fact, our bodies can tell the time by using light and temperature. That's why sometimes we feel even more tired after oversleeping.