The energy will not draining energy away from the healer or her aura, but its coming from the Source itself. The healer will use the Reiki had positions which are making the treatment and Reiki will do the rest. The energy will heal on the four levels of a human: Physical, emotional, mental, and spiritual.
In Reiki I the initiation itself will heal diseases on the physical level of the initiated person. The Reiki I treatments are meant to use at first for self healings. The Reiki I practitioner can give Reiki to others, who are physical present also. In those treatments the practitioner will put the hands on himself or on someone else.