If you feel tired and drained, you are not alone. "Lack of energy" is very popular nowaday.
From TCM point of view, sleeping recharges the body, and is important in maintaining a balance of yin and yang within it. If you sleep too little, the Yin energy will decline beyond the normal range. When Yin energy becomes inadequate, the Yang will predominate. Sleep early and exercise regularly will enhance Qi and blood circulation.
Chinese medicine practitioners divide the day into yin times (11 a.m. to 11 p.m.) and yang times (11 p.m. to 11 a.m.). Each contains six two-hour periods, each one best for certain activities.