My answer may not be scientific or credible (maybe not even valuable) to some, but here goes: I hope you don't mind if this is slightly off-topic. It's NOT faith healing at all but could explain some part of this.As far as the human body goes, IMHO 'natural' healing is not that far fetched to me. My ex-wife was interested in holistic healing and, incidentally, she was also a pediatric homecare nurse. I found the subject is compelling. Some felt it is a placebo effect. I don't try to understand it, but for some type of injuries, healing is what matters.
Injury and the human body...the human body generates energy fields. Neurons transmit information by electrochemical signalling, reaching down the network of the spine. They can be interrupted, or perhaps influenced by, magnetic or external energy fields. Now, the part I don't get (amongst many) is how people can harness their brain power to affect and assist healing; however, I don't deny it can't be done...I just can't say for sure it CAN.
If you're interested in the subject (a former NASA scientist who teaches energy healing), here's a link to website. There is info about healing in there that may interest you: