I would not be surprised if you have not heard of this practice. I don't think that it is well publicised.
I was first introduced to Yoga Nidra a couple of years ago. My yoga teacher played the tape at the end of a yoga session. I was totally hooked from that time on. Yoga Nidra is a most desirably physically relaxed state to experience. To me it was like being in an 'Alpha state'. It was sooo nice.
It is not a meditation and is not a substitute to meditation.
It is a guided practice where the participants listen to a voice for a set period of time, whether it is approximately a 15 minute or a 30 minute session. I have heard both a male and female voice. Most importantly the voice needs to be gentle, slow speaking and caring. One is advised not to go to sleep otherwise the benefits won't be physically felt. (If one goes to sleep and that is perfectly fine because obviously that person needs to sleep.) After asking the participant to think of an intention like I am love, I can forgive, giving and letting go, happiness etc., the voice begins with slow going through the parts of the body like the fingers, then the hand, the arm the shoulder one side the body and then the other side and so on. I found that my body became so relaxed that it took effort to move and sit up at the end.
I was hooked. I knew naught about this practice but after that first time there was no going back. When the opportunity arose, I bought my own DVD on Nidra Yoga on iTunes. This way I can experience Yoga Nidra whenever I feel the need. To me it is a very mindful way of going into a complete zen mode.
Try Yoga Nidra if it comes your way. You may like it too.

Cheers
Angie