Sleep is a complex biological process that allows the body to recharge, repair and renew itself. It’s essential to good health and a strong immune system, as well as a feeling of well-being.

The human body undergoes many cycles of different stages of sleep every night, each a critical part of the overall cycle that allows the brain to rejuvenate and replenish itself. These cycles include REM (rapid eye movement) sleep, NREM (non-rapid eye movement) sleep and slow wave sleep. During these cycles, the brain and other organs undergo various physical and chemical processes to help the body function at its best.

A healthy sleep schedule is essential to getting enough rest at night, says Johns Hopkins sleep expert and neurologist Mark Wu, M.D., Ph.D. If you’re struggling to get adequate sleep, talk to your doctor and request an appointment with a sleep specialist.

Biological clocks govern growth, reproductive cycles and aging, but they also work on a day-to-day time scale, regulating the drive for sleep. This biological clock, known as the circadian rhythm, is controlled by the hypothalamus and other brain structures to trigger the drive for sleep at specific times of the day.

This drive for sleep can be increased or decreased by factors that affect a person’s sleep drive, including sickness, mentally taxing or physically demanding activities, travel, and a change in one’s daily routine. If the sleep drive is not properly maintained, it can lead to fatigue and other negative effects on health and well-being.

The human body’s sleep needs are based on evolutionary reasons, according to sleep expert and neurologist Mark Wu, of Johns Hopkins Medicine. It’s believed that humans have evolved to conserve energy during the day, and sleeping at night provides us with the necessary rest for our bodies to recover from exercise or illness, while still keeping up with other demands of the day.

Sleep is important for brain development and function, and it helps the mind to learn new things and remember information. In addition, it allows the brain to clear cellular debris from the brain that can build up over time and cause damage.

Some of these cellular debris includes proteins and other substances that can lead to inflammation and disease. When the body isn’t able to clear these substances, they can build up and damage the brain cells, leading to memory problems and other mental health issues.

Research suggests that poor sleep causes a variety of health problems, including depression, high blood pressure, seizures, and a greater risk for obesity. In turn, those conditions increase the risk of diabetes and heart disease, and can make a person more susceptible to other illnesses.

Mood and cognitive functioning: People who don’t get enough sleep often experience a lack of motivation, mood swings and trouble learning. This can lead to poor performance at work, school or social activities. In addition, people who don’t get enough sleep may be more likely to have problems with depression and suicidal thoughts.