Sleep is divided into rapid eye movement (REM) sleep and non-REM (deep) sleep stages. During sleep, the body undergoes various activities, which differ based on the specific sleep stage.

Body temperature

Body temperature naturally fluctuates throughout the day, and similar changes occur at night. During sleep, your temperature can be 1 to 2 degrees lower than during the day. As bedtime approaches, body temperature begins to drop, inducing drowsiness. In the deep sleep stage, temperature decreases, making the body feel cooler. Body temperature starts to rise in the morning, preparing the body for wakefulness.

Breathing

Throughout the day, breathing rates vary significantly, depending on activities such as working, sitting, standing, or running. During non-REM sleep (which accounts for about 80% of an adult's sleep time), breathing is slow and regular. However, in REM sleep, the breathing rate increases, often linked to dreaming. Respiration also tends to be shallower and more irregular during this sleep stage.

Coughing

Most people do not cough much during sleep, especially in the REM stage. Sleep suppresses the cough reflex because the chest moves less during REM sleep. At this time, blood oxygen levels are lower and carbon dioxide levels are higher due to decreased respiration.

Heart rate, blood pressure, and blood flow

Heart rate and blood pressure decrease and become more stable during REM sleep. In non-REM sleep, they increase and fluctuate more, similar to daytime levels. Changes in blood flow during this sleep stage can also trigger sexual responses. As dawn approaches, both heart rate and blood pressure gradually rise again.

Brain activity

During non-REM sleep, brain neurons rest, sending only a few insignificant signals. Brain activity increases significantly during REM sleep, sometimes even exceeding daytime levels. Blood flow to the brain and brain metabolism also increase during REM sleep.

While sleeping, the brain restricts body movement, preventing you from acting out your dreams. The brain also utilizes sleep cycles to consolidate memories. Therefore, staying up all night to cram for an exam can be counterproductive.

Other activities

A person can sleep for 7-8 hours without needing to urinate because the kidneys produce less urine during sleep. Concurrently, growth hormone production significantly increases. Your body also produces more thyroid hormones. Cortisol levels, the stress hormone, decrease at the onset of sleep.

Anh Chi (According to WebMD)