its a bit off topic - but i was listening to a neuroscientist discuss with others at the top of their field - the processes going on in our brains when we experience "reality"
i was initially a little surprised to learn that what we experience as reality is actually a simulation of reality the brain runs in real time - based on what it has learned to expect from past experiences and what it knows about
the world - and that is constantly compared to sensory data and updated iteratively where it detects differences between the simulation it has generated and the data coming in from the senses.
i thought it was interesting as it goes a long way to explain some of the things we observe that can be hard to explain otherwise - things like dreams, why the room doesn't spin when we move our heads etc - but also thinks like pain in some patients that have no physical explanation - and no pain in others who, according to their pathology, like a completely shot knee joint - should have lots of pain, but have none.
there is also the famous rubber hand experiment - where people can be made to feel real pain when a rubber hand is hit with a hammer (go to 3:45 for the punchline)
https://www.youtube.com/watch?v=xdxlt68ygt8we know that there are chemicals - like substance P that act as general amplifies of pain signals in the spinal column - but in other cases something seems to get stuck in the simulation process - with the brain expecting pain and therefore continuing to experience it - even when the stimulus is gone.
the pain is however very real