Somnolence is a type of mental fatigue and tiredness that is characterized by an intense desire to sleep, an inability to stay alert during the day, or excessively long periods of sleep. In Chinese medicine, somnolence is associated with the failure of clear yang to reach the head and/or animate the shen. Causes of this failure include localized obstruction to the movement of yang qi, insufficient propulsion behind the movement of yang qi, or insufficient yang qi systemically. Obstruction is typically an excess pattern due to dampness, phlegm, or blood stasis, while failure of propulsion and general lack of yang qi are seen as deficient patterns. In most cases, especially when chronic, there is a mixture of excess and deficiency, and treatment should be adjusted to reflect changes in the person's condition.

It is important to emphasize that somnolence refers specifically to mental fatigue and difficulty thinking clearly, not just to low physical energy. It should be distinguished from other Chinese medical conditions that can cause drowsiness during the day, such as insomnia, depression, and tiredness. Sleep disturbances such as sleep apnea or restless leg syndrome can also lead to marked daytime sleepiness. These problems should be addressed directly. In practice, it can be challenging to determine whether somnolence is the result of a sleep disturbance, as people with nocturnal disturbances may not be aware of them and simply feel sleepy. It is often a partner who notices problems and restlessness in bed.


External Pathogens

A lingering pathogen can obstruct the flow of qi in the body and cause drowsiness. Dampness-related pathogens are often the culprit, particularly when there is chronic dampness in the qi level or damp-heat in the Liver and Gallbladder. This type of dampness may be caused by improper treatment of acute damp-heat infections with cold or bitter herbs, purgatives, diaphoretics, or antibiotics. Damp-heat in the Liver and Gallbladder may also be caused by exposure to damp environments or consuming damp-inducing foods.

Emotional Factors

While emotional factors are not a major cause of somnolence, they can play a role. Repressed emotions can lead to a blockage of Liver qi, which can weaken the Spleen and cause qi deficiency and dampness. Prolonged qi constraint can also slow the flow of fluids in the body, leading to the formation of phlegm and heat. When combined with dampness or phlegm, this can create damp-heat or phlegm-heat, further contributing to somnolence.

Diet and Medications

A diet high in fats, oils, sweets, and alcohol can lead to the production of damp-heat and phlegm, which can cause somnolence. Consuming a diet that is cold or raw, or following restrictive dietary practices, can weaken the Spleen's yang qi and lead to dampness accumulation, eventually damaging Kidney yang. Certain medications can also cause drowsiness, including alcohol, antihistamines, narcotic painkillers, anticonvulsants, benzodiazepines, and beta-blockers.

Exhaustion, Overwork, Age

Excessive physical activity or overwork can deplete the Kidneys, while prolonged exposure to cold temperatures can drain Kidney yang. This applies to general cold exposure, as well as to people who work at night on cold floors, as the cold can enter the Kidney channel through the soles of the feet. Chronic illness and advanced age can also diminish essence, while a sedentary lifestyle combined with intense mental activity can deplete Spleen qi. All of these factors can contribute to somnolence.


Physical trauma to the head, including repeated minor injuries from shaking or contact sports, can cause somnolence. In acute cases, it is important to assess for potentially lethal conditions and provide appropriate treatment. In persistent cases, blood stasis may be obstructing the flow of clear yang in the head, leading to somnolence.