Sleep is very necessary for every living being. Without sleep, man as well as other beings cannot, live. Of all the joys that the world provides, sleep is the most rewarding. All the rest are arid and dry, trivial and wasteful. (Sutra Vahini, p.51)
The world is the creation of your mind; go into deep sleep; it is negated! That is why sleep is said to be a form of Samadhi, when the dhi (intellect) becomes Sama (balanced), merged in equanimity. Arjuna said, ‘Lord! Your maaya is difficult to overcome!’ The maaya is His leela (sport). So, take refuge in Him, for, He alone can save you from the machination of His creation. (SSS Vol. 10, p. 88)
What you have asked is linked closely to the age factor. Babies need 22 hours of sleep. They are awake only for drinking milk and for being bathed. For children between the age of 5 and 12, ten hours of sleep is essential. Those between 12 to 32 years of age require seven or eight hours of sleep. There is another fact to be explained. You all go to bed in the hostel at, say, 9.00 P.M. The wake-up time is 4.00 A.M. You have slept for seven hours. And yet, you may have noticed that quite a few boys doze away in the classes! The cure for this ailment is to sleep early and to wake up early. But do not wake up early as 4.00 A.M. Instead, you can still get your seven hours of sleep by sleeping at 9.30 P.M and waking up at 4.30 A.M. This will ensure that you do not feel sleepy in the classroom. After your dinner, spend some time in studying. Then ruminate over what you have studied and go to sleep by 9.30 P.M. After a few days, you will get up at 4.30 AM. by yourself. This habit will also gradually prevent you from feeling sleepy during the daytime.
Students should not sleep during the daytime. Elderly people can sleep during the day. At the same time, students must see that they do not rush to the college immediately after their lunch. Recline on the chair for some time after lunch and closing your eyes, take a little rest. That is why it has been said. ‘Walk a while after dinner, sleep a while after lunch’. After eating, the blood rushes from head on to the lower parts of the body. This induces some drowsiness in you. It is not proper to walk at that time. It is better to close your eyes and take rest until the speeding circulation reduces to normal speed. Those who are between 35 and 50 years of age can do with just five or four hours of sleep. Forgetfulness sets, in if they sleep for more time. Hence, forgetfulness does not come with age. It comes due to sleeping for excess time.
Once a person exceeds 70 years of age, he must have only 4 to 3.5 hours of sleep. I am now 70 years. But I do not sleep even for a minute. None of you know that. However, I close my eyes. This too is because I cannot work at that time when everybody is sound asleep. They will all then know that I do not sleep. For the sake of the public, I close my eyes and am lost deep in my own thoughts. Nobody has seen me sleeping till now. Many a times, when we go on long distance journey by car, I remain seated in the car for the entire course of the journey. Sometimes, the driver may feel sleepy and to keep him awake, I tell interesting and enjoyable stories! I do not know what is the meaning of sleep. I also have a strong wish to see how sorrow, loss and worry look like. They are total strangers to me. These are all the qualities of Divinity.
(M, p. 209-210)