Just nearby, in the ajanta caves, in the last cave there is a sculpture of gautam buddha sleeping. That pose has become known as the "Lion's pose" Because the lion also sleeps on its side without moving. When gautum buddha was alive, he used to sleep in same posture, whole night. He wouldn't move from side to side or even an inch from his sleeping position. One of gautam buddha's disciple named ananda was very much troubled because of this. Every night he could see that buddha was still. Sometimes, in middle of night he would wake up and would see that buddha was still in same position, absolutely still, just as he had always been. One night he couldn't resist his curiosity and went to buddha while he was sleeping. He wake him up and said, "I know it's not good to disturb you at night because whole day you have been walking and teaching but I couldn't wait for morning to ask you this.for twenty years I have been watching you, I have waited for long but know I have to ask to you about it anyway.please tell me, how do you manage to remain in same posture that you go to sleep in, in same posture for whole night? do you sleep or do you simply go on keeping that posture.because I have to move continuously, I can't sleep still whole night."Gautam buddha said. "I have found the right posture. now, there is no need to change it and I am awake as anyone even when my body is asleep. I have found the right posture for body but you are still searching for it.it is not simply a question of tossing and turning the body. it is because your mind is tossing and turning.I have gone beyond - there is no mind when I go to sleep. the body simply lies down like a corpse. have you even seen any corpse changing its posture?" It is your mind. Once your mind is at rest, once it disappears, your body can remain asleep but your inner eye, your inner sensitivity, your awareness, can remain burning like a small flame - not only watching your body but also watching the silent mind and the stillness surrounding you. 
The enlightened man cannot sleep in the same way that the unenlightened one sleeps. When the unenlightened man sleeps, he is simply unconscious where as the enlightened man sleeps but he is not unconscious. 