Sleep

Sleep is a natural state of rest that almost every animal needs. During sleep, the body slows down and the mind shifts into a different kind of activity. Your eyes close, your muscles relax, and your breathing becomes slow and steady. But your brain stays busy. It sorts memories, repairs cells, and gets you ready for the next day.

Kids need more sleep than adults. A 5th grader needs about 9 to 11 hours each night. A baby may sleep 16 hours a day. A grown-up usually needs 7 or 8 hours. Adding it up, the average person spends about a third of their life asleep. By age 75, that is roughly 25 years of sleeping.

Sleep happens in stages that repeat through the night. In light sleep, you can wake up easily. In deep sleep, your heart rate and breathing slow way down, and the body releases chemicals that help you grow and heal. Then comes a stage called REM, short for rapid eye movement. Your eyes flick around under your eyelids, and your brain becomes almost as active as when you are awake. Most dreams happen during REM sleep. A full cycle takes about 90 minutes, and you go through four or five cycles each night.

Why do we dream? Scientists are not sure. Some think dreams help the brain practice solving problems. Others think they help store memories or work through feelings. The honest answer is that we do not fully know yet. Dreams remain one of the biggest mysteries in brain science.

Going without sleep is bad for the body. After one rough night, you feel grumpy and have trouble paying attention. After several nights, your immune system gets weaker and you are more likely to get sick. Long-term sleep loss is linked to heart problems and trouble with memory. Almost no animal can skip sleep for long. Even fruit flies need it.

Different animals sleep in strange ways. Giraffes sleep only about two hours a day, in short naps. Bats and koalas sleep more than 18 hours. Sharks have to keep moving to breathe, so some of them rest while still swimming. Dolphins shut down half of their brain at a time so they never fully sleep at all.

Good sleep habits help. A dark, quiet room, a steady bedtime, and no screens right before bed all make falling asleep easier. Your brain rewards you for it the next morning.