The Thai Forest Ajahn Maha Boowa made of use of contemplating his pains. He describes heavily pains in the book Arahattamagga-Arahattaphala and how he probed into it with mindfulness and wisdom.
A short fragment (page 20-21):
"Although the bodily pain was obviously very strong, I could see that the citta was calm and unafflicted. No matter how much discomfort the body suffered, the citta was not distressed or agitated. This intrigued me. Normally the kilesas join forces with pain, and this alliance causes the citta to be disturbed by the body’s suffering. This prompted wisdom to probe into the nature of the body, the nature of pain and the nature of the citta until all three were perceived clearly as separate realities, each true in its own natural sphere.
I saw clearly that it was the citta that defined feeling as being painful and unpleasant. Otherwise, pain was merely a natural phenomenon that occurred. It was not an integral part of the body, nor was it intrinsic to the citta. As soon as this principle became absolutely clear, the pain vanished in an instant. At that moment, the body was simply the body—a separate reality on its own. Pain was simply feeling, and in a flash that feeling vanished straight into the citta. As soon as the pain vanished into the citta, the citta knew that the pain had disappeared. It just vanished without a trace".
Highlighted by me.
I tend to believe this is true. I have not realised this but i i think i see how, indeed, the citta judges feelings as painful and pleasant. This it its strong habit. Maha Boowa seems to have made a jump here in a state where feeling is just feeling and no judgements takes place.
Is pleasentness and painfulness something that is just a results of our human nature, a conditioned way of experiencing things. Can we go beyond? Maha Boowa seems to suggest that it is possible. I think also other masters in other tradition do.