As an analogy. When you’re stretching your muscles, you’re generally not actually elongating any part of your body, instead you’re teaching your nervous system that it’s safe to move your muscles in the range you’re stretching into.
Most people get to experience acute back pain in their life, and will notice how this can cause your entire back to freeze up, even well past the point of where the actual thing that caused the pain has been healed. This is the nervous system protecting your back from hurting itself. Making it a necessary part of rehabilitation to do stretches to show your body that the range of motion is safe again.
In the same kind of way, actively working on mentally overcoming symptoms that were your body’s reaction to real disease or trauma that has since passed, can have very real effects.
This could be in the form of meditation, therapy or even faith healing(!) [0]
[0] see derren brown talk about his experiences doing faith healing as a skeptic https://youtu.be/CCzzaDwUuDk time stamp 22 minutes 18 seconds