While a one time Reiki treatment is beneficial, bringing a sense of calm and peacefulness, and possibly producing some short term physical benefits, too, the best results come through having a course of treatments. Most people find that 4 to 6 sessions on weekly intervals is best. Energy healing in this way is accumulative and multiple sessions close together leads one to peel the layers off and set up the scene for a breakthrough.
The effects of Reiki are cumulative, so having a course of treatments helps to produce long-term beneficial changes on many levels.