Based on the holistic approach, TCM views the human sleep-wake cycle as a dynamic yet integral physiological state, with physicians using unique theories like yin and yang, qi circulation and spirit activity to understand and explain the sleeping process.

1. The Yin Yang Natural Rhythm
Sleeping recharges the body, and is important in maintaining the balance of yin and yang within it. The regular succession of daily or seasonal cycles is the primordial expression of the waxing and waning of yin and yang in the universe. The human body is programmed to live in harmony with the rhythm of nature as the Lingshu (The Vital Axis) states: "When yang qi is at its limit and yin qi is abundant, one's eyes are closed. When yin qi is at its limit and yang qi is abundant, one is awake." We naturally go to bed at the yin predominate time (night) while wake up at the yang predominate time (day).

2. The Internal Energy Cycle
On a daily basis, qi (vital energy) follows a specific time schedule and pathway to circulate inside the body. TCM believes that qi is more prevalent in different meridians at different times. For example, physicians use the "Daily Qi Current of the 12-hour Division" as one of their clinical guidelines. The sleep-wake cycle is regulated by this energy cycle, in particular by two types of qi – protective qi and nutritive qi.

Yin Heel Vessel	Yang Heel Vessel

Protective qi has a yang property because it has more functional characteristics such as fighting against evil invasions or controlling sweating. Protective qi circulates through the body 50 times per day. In the daytime, it flows along the yang meridians, which starts from the bladder meridian, passes through the small intestine meridian, gallbladder meridian, triple burner meridian, stomach meridian,to finally reach to the large intestine meridian. From sunrise to sunset, protective qi repeatedly flows around the yang meridians 25 times, which enables the body function to be active and remain awake. At nighttime, protective qi enters the yin meridians and circuits around and through the kidney, heart, lung, liver and spleen respectively 25 times. There are two extra meridians, the Yin Heel and Yang Heel Vessels (see graphics) that help strengthen the links between the meridians, and also govern the opening and closing of the eyes. It is also claimed that the acu-point qing-ming (Bl1), located at inner canthi of the eyes, are where protective qi flows inside and outside of the body.

On the other hand, nutritive qi has a yin property as it can form into materials needed by other parts of the body. Nutritive qi follows the regular meridian flow chart and continuously circulates through the body in a daily cycle. According to the Huang Di Nei Jing (The Yellow Emperor's Medicine Classic), the flowing pathways are the lung meridian - large intestine meridian – stomach meridian – spleen meridian – heart meridian – small meridian – bladder meridian – kidney meridian – pericardium meridian – triple burner meridian – gallbladder meridian – liver meridian – Governor Vessel – Conception Vessel. Both nutritive and protective qi share the same origin, but they flow in opposite directions. The movements of these two types of qi work in a coordinated manner to maintain a harmonious balance.

3. The Shen (spirit) Activity
The sleep-wake cycle is also part of shen (spirit) activities. Shen in Chinese medicine refers to thought, state of consciousness and mental functions that keep the mind sharp and alert. It is the highest authority of the physical body that orders it to rest or work. In coordination with the natural rhythm, shen hides in the organs at night for recharging, and comes out during daytime to exert its duties. Sometimes when shen is too excited, for example during emotional conflict, sleeping problems occur.

In conclusion, normal sleep is the result of the harmony of yin and yang in the body; yang governs awakening, yin governs sleeping. When insomnia develops, it is due to yang not interacting with yin, in other words, the internal environment has been disturbed and becomes overly excited leading to a restless state.

The daily qi current chart

Arm Leg Yin/Interior Yang/Exterior   Yang/Exterior Yin/Interior Arm Tai Yin Lung Meridian (3am - 5am) Arm Yang Ming Large Intestine Meridian (5am - 7am ) Leg Yang Ming Stomach Meridian (7am-9am) Leg Tai Yin Spleen Meridian (9am-11am) Arm Shao Yin Heart Meridian (11am-1pm) Arm Tai Yang Small Intestine Meridian (1pm-3pm) Leg Tai Yang Bladder Meridian (3pm-5pm) Leg Shao Yin Kidney Meridian (5pm-7pm) Arm Jue Yin Pericardium Meridian (7pm-9pm) Arm Shao Yang Triple Burner Meridian (9pm-11pm) Leg Shao Yang Gall Bladder Meridian (11pm-1am) Leg Jue Yin Liver Meridian (1am-3am)