Sleeping in a different posture.

 Head should not touch the floor. One hand should be folded. Right arm is the most preferred. Elbow must touch the earth. Neck should rest on the hand. Eyes should be closed. Deep sleep is more recommended. This posture should be recommended. Should be fully trained and well practiced for this purpose. You might have seen Lord Buddha and Maha Vishnu sleeping in this posture in this idol form in the temples dedicated to them. This is a way to avoid ants and similar insects entering the ears of yours in dense forests. You will not be able to obtain cotton balls to prevent the insects getting in side your ears in those environments. All types of ferocious animals will be on the move there. So your ears should be sharp for listening any moves. While the eyes are being closed ears become more sharpened. Even during the deep sleep too, you must be alert always.

This too becomes a kind of yoga practice.