I have been practicing Sudarshan Kriya and meditation for more than six years now, and yet the efficacy of these techniques never fails to amaze me. There is a good reason why we refer to these techniques as "spiritual practices," meaning they are not theories or hypotheses waiting to be proved. Instead, they are tried and tested methods that have been used since centuries to relax the mind, refresh the system and dive to the source of thought.
Very often, the human mind chooses quantity over quality. So it baffles us when we hear that twenty minutes of meditation can be more restful than eight hours of sleep. The math does not match up! Well, it needs to be experienced. It has happened to me on multiple occasions that I wake up after 7-8 hours of sleep, feeling hardly rested. My limbs feel sore and heavy, and I cannot shake off the dullness in my mind. On such mornings, it is tempting to fool the mind into thinking that lying in bed for those five extra minutes will make all the difference. Does not work, really. But spending an hour on yoga, Sudarshan Kriya and meditation will most certainly help. One such morning, I just about managed to make myself sit for my daily practice. And an hour later, I could hardly believe how different I felt. The body felt much lighter and my legs had lost their soreness. The mind felt calm and completely relaxed. The draining fatigue of the night before had been replaced with an incredible sense of energy and clarity.
I remember listening to a talk by Sri Sri where he explains that the more subtle an object/entity is, the tougher it is to describe. This, in my opinion, perfectly describes the experience of Sudarshan Kriya and meditation. But I have tried to do that... and you can read it in the lines above! Or you can go and experience it yourself because my words can barely convey an iota of the beauty and magic of these spiritual practices.