Answer

Scientifically, it is found that one full cycle of sleep is of four hours only. But, after completing one cycle, due to one’s laziness he remains in lying position and goes into second cycle of sleep of next four hours. Thus, mistakingly, even medical science recommend minimum of 8 hours sleep!

The reason for this laziness is because, the cycle time of four hours sleep is not being commonly selected as the most appropriate one which, is from 11 p.m. to 3 a.m. From scientific research, it is found that during these four hours maximum blood remains in liver, while rest of the body remains with less than average blood normally body contains. It is because of that reason body , brain in particular needs full rest. Therefore, it is essential to have full rest of the body so that liver will function in best possible manner. To get both the functions satisfactorily performed viz., rest to brain n body and best liver working, one should sleep from 11 p.m. to 3 a.m.without any disturbances. If this cycle is well maintained then only, one cycle of sleep is sufficient for living a normal day to day life during the day.

In the light of above fact, probably Yogis were aware of this and must have found it by hit and trial to fix 11 p.m. to 3 a.m. for sleep. After 3 a.m. blood starts going, in excess quantity, to lungs which, remains there in excess upto 5.00 a.m. . That is why Yogis devot this time of 3 a.m. to 5 a.m. for Pranayamas, Yogasanas and Meditation etc.