I'm guessing healing magic works in much the same way then. It uses the patient's own stores of energy to heal the tissue at a faster rate. As a side effect, they get the brunt of the pain and intense (possibly lethal) exhaustion. You could possibly also use your own body (or any bystander's) as a source of energy as well, given that you have that level of control over it.

Dark healing magic... Heal somebody so hard they develope cancerous tumors... You could even theoretically grow tissue to attatch itself to solid objects. Like armor... Extraneous mutations not withstanding.