Pranayama is mostly defined as breath control. The word itself translates as the expansion of the prana (vital energy/life force). In a very simple way this also can be explained as practising different breathing techniques on a regular basis.
“Yoga Nidra, which derived from the tantras, is a powerful technique in which you learn to relax consciously. In Yoga Nidra, sleep is not regarded as relaxation. People feel that they are relaxing when they collapse in an easy chair with a cup of coffee, a drink or a cigarette and read a newspaper or switch on the television. But this will never suffice as a scientific definition of relaxation. these are only sensory diversions. True relaxation is actually an experience far beyond all this. For absolute relaxation, you must remain aware. This is Yoga Nidra, the state of dynamic sleep.
Yoga Nidra is a systematic method of inducing complete physical, mental and emotional relaxation. The term Yoga Nidra is derived from two Sanskrit words, yoga meaning union or one-pointed awareness and Nidra which means sleep. During the practice of yoga Nidra, one appears to be asleep but the consciousness is functioning at a deeper level of awareness. For this reason, Yoga Nidra is often referred to as psychic sleep or deep relaxation with inner awareness. In this threshold state between sleep and wakefulness, contact with the subconscious dimensions occurs spontaneously.
In Yoga Nidra, the state of relaxation is reached by turning inwards, away from outer experiences. ıf the consciousness can be separated from external awareness and from sleep, it becomes very powerful and can be applied in many ways, for example, to develop the memory, increase knowledge and creativity or transform one’s nature.”
Swami Satyananda Saraswati, Yoga Nidra