When it comes to the health of your heart, brain and body, sleep is one of the most important things you can do. Yet many people don’t get enough good quality sleep to function at their best. This can lead to a number of health problems including depression, diabetes, high blood pressure, heart disease and obesity. Getting a good night’s sleep can improve your mood, concentration and memory. It can also help you make better decisions and feel more emotionally stable.

While you’re sleeping, your brain is busy with a host of tasks. It is preparing for learning, remembering and analyzing information, repairing cells, strengthening immune system and regulating hormones. But that’s just the tip of the iceberg when it comes to what happens during a night of restful sleep.

Scientists are only beginning to uncover all the benefits of sleep and why we need it. In addition to repairing the damage from our daily lives, research shows that sleep supports healthy brain function, helps maintain a healthy metabolism and weight, and keeps your body strong, healthy and active. In children and teens, sufficient amounts of sleep are vital for normal growth and development.

There are two processes that regulate your sleep: circadian rhythms and your homeostatic drive to sleep. The former determines when you go to bed and wake up, while the latter increases your urge to sleep when you’re sick or physically or mentally taxing activities. Having a discrepancy between these systems can cause problems like jet lag and insomnia.

The first phase of sleep is called non-rapid eye movement (NREM) or light sleep. During NREM, muscle tone decreases and the eyes stay closed. You may have bursts of rapid brain waves (sleep spindles). You will usually remember some dreaming. If woken during this phase, you may have brief moments of feeling as if you’re falling or experiencing a quick jerk (called a hypnic jerk). These are completely normal and harmless.

You spend less time in NREM and more time in REM sleep as the night goes on. You’ll experience the most intense dreams during this period of sleep. In REM sleep, the muscles in your face and body become more active, and the eye movements are similar to those during wakefulness. The blood flow to the brain increases, and your breathing and heart rate increase, too.

While you are sleeping, your immune system is working to fight infections and illnesses. Research suggests that the more rested you are, the stronger your immune system will be. In fact, well-rested adults are more likely to survive from influenza than those who are not. Getting adequate sleep can even make your vaccines more effective.