The Yin Period indicates the time between 3:00a.m.to 5:00 a.m., when the lung channels are on duty. This period is a process of body flowing switch; in other words, body flows being quiet switch to being active, and it requires deep sleep. The time people in deep sleep are usually from 3:00 a.m. to 5:00 a.m, and this period is exactly the time when a person's body vital energy and blood switch from being clam to being active. This process requires our bodies to be in very deep sleep for it to be fully completed. Here, SWITCH is exactly a process of internal body natural purifying or transforming.

It is better for older people, whose heart functions are not as good as younger people, not to get up too early in the morning, nor to work out but instead, to get out of bed slowly and later than others. Evening is the time when Yin energy is spooky, or hazy, that one may move around to shake off the hazy. However, the morning is when the Yang energy grows and develops; therefore, it is a best to let the nature takes its course.