This is a brief, preliminary version of Yoga-nidra (not a full Yoga-nidra).  It is a way of taking quick rests during the day for a few minutes.  It may be done sitting in a chair, resting on a sofa, or lying down.
Here is the synopsis:
1) Close your eyes, relax, and be aware of your entire body from head to toe.
2) Breathe diaphragmatically as though the breath is flowing from top to toes,  and toes to top.
3) Bring your awareness to the Ajna Chakra, and exhale and inhale three times
4) Bring your awareness to the Vishuddha Chakra, visualize an immaculate full moon there, and exhale and inhale three times.
5) Bring your awareness to the Anahata Chakra, and exhale and inhale three times.
6) Feel as if there is a Cave in the Anahata Chakra, and breathe as if you are inhaling into the Cave and exhaling from your toes.
7) Breathe with no thought, no mantra  –  but only the awareness of the breath and the prana flow.
8) When you feel rested, open your eyes and gently sit up.