Getting a good night’s sleep on a regular basis is vital to your health. It helps you maintain a healthy weight, stay alert and productive during the day, fight off illness, and keep your brain functioning properly. It also contributes to a sense of well-being, and can improve your mood. Sleep deprivation is linked to a variety of serious conditions, including heart disease and high blood pressure. It can also affect how well you think, react, work and learn.

Scientists are only beginning to understand how important sleep is, and there’s still a lot they don’t know. But one thing they do know is that your body and brain go through a series of distinct phases during the night, called sleep cycles. Each cycle takes about 90 minutes to two hours. During these cycles, certain parts of the brain power down, but other areas remain surprisingly active.

The first phase of the cycle is non-rapid eye movement (NREM) sleep, which is when most of your dreams occur. During this time, your breathing and heart rate slow down, your muscles relax, and the body restores its energy levels.

Next comes REM sleep, which is when you dream again. It’s thought that dreams help you process new information and memories, and that the REM stage allows the brain to clear away old and unneeded materials. REM happens about five times during the night. Adults spend about a third of the total time asleep in REM, while babies spend half of their time in this stage.

The last stage of the cycle is deep sleep, which consists of several shorter periods of NREM sleep. Deep sleep is crucial for maintaining a strong immune system and for helping your brain get rid of toxins. In fact, researchers found that a certain protein that builds up in the brain and is associated with Alzheimer’s disease is removed twice as fast during sleep as it is when you are awake.

There are several theories about why we need to sleep, but it’s important to remember that sleep isn’t just a time when your mind and body “shut off.” Instead, during sleep, your brain and body engage in many vital activities.

The pace of modern life can make it difficult to get enough sleep on a regular basis. Insufficient slumber is linked to a variety of health issues, from weakened immunity and a weaker immune system to increased risk for heart disease and high blood pressure to memory loss, depression and mental illness. It can also affect how well you perform at work or school and impact your ability to get along with others. It can even increase your risk of accidents and injuries, especially if you’re driving. For these reasons, it’s important to prioritize your sleep and find ways to ensure you’re getting enough of it.