Healing may not be as old as the hills but it is likely as old as humanity. As humans we have a little something extra that doesn't exist in the rest of nature. We have a human energy field. Unlike the rest of the animal world we are capable of going against our natural instincts. This, however, is a recipe for disaster. When our good, loving energy becomes conflicted--let's say from physical abuse--our energy shifts in order to protect our self. Instead of feeling loving and confident we will likely become fearful, untrusting and angry. You get the idea. Life situations can cause our energy flow to deviate from it's natural free-flowing state. In construction, we would call this a dam. A dam is intended to block the flow of water. Beavers have utilized the technique to create a favorable habitat for themselves. Humans have built dams to protect property, to create electricity, or to create water storage. Within ourselves, however, dams aren't a good thing.
Our energy needs to flow properly. We normally won't notice it for some time because we become accustomed to it. Eventually, however, the dam will cause physical issues. You see--mental, emotional, spiritual issues aren't as tangible. We can't necessarily see or touch them. They are easy to dismiss. But of course, they are all part of a whole being and eventually lead to physical issues much the way a beaver dam changes the lay of the land by blocking the flow of water.
Energy is the source of everything. It is the thing that unites us. It is the thing that gives us life. When it is transformed in a negative way it gives us pain and suffering. When it is transformed in a positive way it gives us healing.