Sleep has long been a mysterious aspect of the human condition, but in recent decades scientists have discovered its role in a wide range of bodily functions, including metabolism, learning, memory and mood. Insufficient or inconsistent quality of sleep can have major health consequences and affect how well we think, react, work and learn. It can also cause many different health problems, including obesity, diabetes, depression, heart disease and a host of others.

At the behavioral level, sleep is usually defined as a recurring period of inactivity that is distinguished from wakefulness by meeting several behavioral, motor and sensory criteria. In addition, it is characterized by the characteristic posture of horizontal repose in humans and most animals and by the absence of overt goal-directed behavior. In experimental studies, the presence of specific brain patterns of electrical activity is commonly used to distinguish sleep from wakefulness, and these patterns are usually seen in a state of rem sleep.

In humans, a typical night of sleep includes four to six periods of non-rapid eye movement (NREM) and one or more periods of rapid eye movement (REM) sleep. NREM sleep usually begins with a period of light NREM sleep or what is called stage 1 of NREM sleep, and ends with a deeper phase known as NREM stage 2. During REM sleep, the brain and body are more active than during any other sleep stages. This phase of sleep is associated with dreaming.

Throughout the day and night, the brain signals to the body when it’s time for sleep. The body is then able to respond appropriately, such as by decreasing muscle activity and resetting the internal clock, which in turn controls hormone production. These hormones play an important role in keeping the body healthy, ensuring that we are at the right energy level for all activities.

While you are sleeping, the brain is recharging and repairing itself. It also plays a role in the formation of memories and emotions, and helps to regulate blood pressure, blood sugar and hunger. During sleep, the immune system is also activated, and a good night’s rest is crucial for healing any wounds.

It’s important to get enough sleep, especially as you grow older. Insufficient or inconsistent sleep can cause stress, which can trigger the production of a hormone called cortisol that can keep you awake. This can lead to a wide range of health issues, such as heart disease, obesity, high blood pressure, depression and anxiety.

The best way to ensure you’re getting enough sleep is to establish a regular routine. Aim to go to bed and rise at the same time every day, and make sure your bedroom is a comfortable place to sleep. It may also be helpful to relax before you go to bed, such as by having a bath or reading a book.