Quote from ACIM Text Chapter 2, Section 5 - The Function of the Miracle Worker.

Magic is the mindless or the miscreative use of mind. Physical medications are forms of "spells," but if you are afraid to use the mind to heal, you should not attempt to do so. The very fact that you are afraid makes your mind vulnerable to miscreation. You are therefore likely to misunderstand any healing that might occur, and because egocentricity and fear usually occur together, you may be unable to accept the real Source of the healing. Under these conditions, it is safer for you to rely temporarily on physical healing devices, because you cannot misperceive them as your own creations. As long as your sense of vulnerability persists, you should not attempt to perform miracles.