Reiki is a Universal energy that can be channeled from a person to another person to heal and cleanse. Reiki is unlimited in uses, you can Reiki your car, plants, animals and so on. When healing another person, you also heal yourself as the energy flows into your Crown chakra through your body to your hands to the recipient.
I was attuned, Reiki I, mid-summer in a river (doesn't have to be, that was just where it felt right for me and my Reiki teacher) and from that experience I have grown substantially, in all aspects.
A certified Reiki III master, also my father's girlfriend and one of my close friends, attuned me. She did so free of charge though not many Reiki masters will do such. My experience was beyond words to relay in regards to how I felt, but I will tell you what I saw.
Sitting in a river, a sacred bubbling spot where an underwater stream feeds the river. Reiki can be done by laying hands on specific spots of the body, holding hands above the spot but not touching, and higher levels can send Reiki over distance. For this my teacher did both touch and hover. I got into a meditative state. A large ball of energy appeared to my right, growing larger and different hued with each ring. My peripherals saw something blue moving to my left, and I broke my concentration in excitement. The rainbow orb dissolved and the balls of blue that ran on top of the water would only appear from the corner of my eye. I watched them for a little while until I clearly heard "Come back to the healing." I calmed down then went back to the meditative state.
Black and red of closed eyes. From the Universe, a black little line came towards me. It turned to a red line, then grew bigger as it got closer then went through me. Another came. And another. When the waves stopped, I suspected the attuning was done and opened my eyes halfway. I had to close them again, it looked like the world was spinning. At what time my teacher moved away from behind me I'm not sure. This was such a moving experience, I utilize my channeling every day. Before Reiki I healed with my own energy, making myself tired and irritable. With Reiki, and hour of it does not tire, but rather, energizes me. I hope you consider looking into this ancient practice, I have grown from it and its only been a couple months since my attuning.
Usui Reiki by Peggy L. Jentoft can be read online, this is the manual referred to me by my Reiki teacher and covers traditional and contemporary methods of Reiki and has chapters on chakras, energies, auras and all the basics for Reiki I. I cannot give you a reference for higher levels because I am not there yet but this book is a fountain of knowledge in itself.
