Yes Azhar You are correct about that the spirits that you invole wether consciously or not [in the case of spells] can drain your energy. We all seem to forget our true sources of like hence power. Earth and God.
Now with working on people and uising the earth you much be connectd via the earth chakras in the arches in the feet.
Using god as a source of energy and his people angels and what not is a good alterative, but this shows an under lying conflit that must be resolved that of which is the healer him or her selves.
To be an efficent healer would it not make sense that you would have to be sufficently developed in you own energy system.
I believe that a person wishing to undertake healing should heal them selves and feach a state of zen so to speake [ballance]
Primary centers are good to know and can be master to a point of being in that state but that can lead us in to a false illusion of perfection where as there and many other energy points that help in the development of the etheric body and thus effecting the spirit of the person to excell them to greater heights
this post of mine albeit very lengths outlines and points out the minor charas and related information
I would recomend it for reading
DK