I have this theory. ( not in the scientific sense
)
I think that the brain is capable of all sorts of things sometimes, on an unconscious level.
It regulates our bodies and sometimes when a person is ill, everything can start packing up, kidneys etc.
The positive side is a cancer going into remission or the negative is one, being really aggressive.
Some people when the lose either a partner or a routine, it's like they give up on life, or an underlying condition takes off.
Prayer might influence the brain in some way in some people.
sometimes things appear to work and sometimes they don't.
Perhaps sometimes under some conditions, some people's bodies have an ability others don't.
Whether you can curl your tongue or not is a genetic thing ( you either can or you can't)
Maybe the ability of the unconscious brain to heal the body, is also genetic.
The ones most noticeable are the ones considered untreatable.
It would explain why it is inconsistent.
Perhaps we need to know more about the brain and what it can do.