Although the contact between the human body and the outside world is weakened or even disappears during sleep, the human organs are not in a static state, and various physiological functions of the body, such as sensory, motor, and autonomic functions, are in regular activity with the change of sleep depth. EEG activity shows that the brain activity during the sleep phase shows a series of actively regulated periodic changes. Internationally, sleep is divided into two different phases according to the EEG performance, eye movements and changes in muscle tone during sleep, i.e., non-REM sleep and REM sleep, which, like all phases in medicine, are different but cannot be separated. Non-Rapid Eye Movement sleep (NREM): starts with sleep onset and progresses gradually as sleep deepens. This stage is subdivided into four phases, with stage 1 being sleep onset, stage 2 being light sleep, stage 3 being moderate sleep and stage 4 being deep sleep. From the onset of sleep, the person’s breathing becomes shallow, slow and even, the heart rate slows, the blood pressure drops, the whole body muscles relax (still able to hold a certain position), and there is no obvious eye movement. During this period, normal people have a major postural adjustment once every 20 minutes on average, and some people even have a postural adjustment activity every 5 minutes. We sleep in one position and wake up in another generally. So it is normal for children to have turning movements during sleep. Rapid eye movement sleep (REM): After non-REM sleep lasting about 90 minutes, the body enters REM sleep, where the body’s sensory function is further reduced, muscles are more relaxed, tendon reflexes disappear, and the eyes turn rapidly. During this stage, blood pressure is higher than during slow eye movement sleep, breathing is slightly faster and irregular, body temperature and heart rate are also increased, and the metabolic functions of all organs in the body are significantly increased. Some muscles in the body may twitch, such as the facial muscles and some muscle groups in the limbs, which may be manifested as a sudden shaking of the body, and the penis may become erect. The phenomenon of muscle twitching is manifested in infants as sucking action, smile, hand and foot movement, and throat sound, etc. It is normal for infants, especially newborn infants, to have a burst of faster breathing and even throat popping during sleep, that is in the REM phase of sleep, after a period of time into the NREM phase of the child’s breathing will be very smooth, and we even need to watch carefully to notice the child’s smooth breathing. During this period, the pituitary gland secretes more growth hormone, so it is important to ensure that children’s REM sleep is important for children to grow taller. Moreover, this stage is also the time for dreaming. Studies have concluded that 74-95% of sleepers who are awakened during this stage complain of dreaming and can remember the content of their dreams, whereas during non-REM sleep, only a small percentage complain of dreaming. Some studies have found that REM sleep improves creativity, so let’s learn to dream! Figure 1: Sleep phase image from Baidu in the NREM sleep period lasts 80-120 minutes after the first REM sleep, lasts a few minutes into the next NREM sleep, forming a cycle of NREM sleep and REM sleep cycle, on average, every 90 minutes there is a REM sleep, the closer to the late sleep REM sleep duration gradually extended, each time up to 10-30 minutes. So people will dream more in the early morning. The above two sleep phases occur 3-5 times in a single sleep cycle, which means that people go through several cycles in a single sleep cycle. The cyclic transition between the two sleep phases shows that the sleep process does not continue from shallow to deep as soon as you fall asleep until dawn, but alternates between deep and shallow sleep. The stages of each cycle are not necessarily complete, but they all start with stage 1, and the depth of sleep in each cycle becomes shallower in the early morning and no longer reaches stage 4. If you are disturbed during sleep, you need to start the cycle from stage 1. In general, REM accounts for about 20% of the whole night’s sleep in adults, 75% in premature babies and 50% in newborns, and the proportion of REM gradually decreases and stabilizes after the age of 10. So, it is normal for children to sleep restlessly because TAs have a higher percentage of REM! Figure 2: Sleep phases Image from Baidu Because sleep consists of different phases, the REM phase is not “restful” because of increased physical activity and dreaming during the whole sleep process. This is true for adults, but it is normal for children to be more restless because of the higher percentage of REM phases. Therefore, children wake up during the night unless they have a need, such as a hungry tummy, a diaper that needs to be changed, a physiological need or an illness. The most important thing we should do is: do nothing!