Early Buddhist Texts (EBT) are fairly non-religious, e.g. see the Thai forest tradition/BSWA talks
this school of thought even often ignores a fair portion of the abhidama texts ("about dhamma", the meta commentaries) that started to form a number of years after the death of the Buddha
anecdotally, I had a late PoTS (postural static tachycardia syndrome, blood vessels don't autonomically constrict correctly depending on posture) diagnosis, then hypermobile EDS (tissue that's more floppy)
I realised on body scan relaxations that
a) a pain arose in most body parts as I tried to gently allow a letting go of tension in that part, like something I had to shake off, kinda like DOMS though also similar to the body tension pain I get as a certain kind of autistic person repeatedly failing a task,
n b) that any however much relaxed part very quickly subconsciously tensed up once again within seconds of my focus moving to a new part. chronic tension from 1) needing to tense for blood to better flow, n 2) trauma. I've had masseurs tell me my muscles fight back, n fwiw prolapse op from the EDS, n I get pregabalin for the tension pain
"immersion" as a better translation than "concentration", suggested by Sujato
(can't remember their exact chat about that EBT translation compared to Bodhi or Brahm in whichever of the miriad of Buddhist Society of Western Australia talk/retreat videos I heard it discussed)
mindfulness of body sensation, feeling, thought and principle bringing enough equanimity to start ignoring it all really easy, though the moral aspect can't be separated because doing not wholesome actions will leave you thinking about them
https://skullvomit.bandcamp.com/track/ai-generated-music-poo...
reply