(this post keeps tagging as military and war each time i post it and idk why im very sorry if that happens this time)
so, i'm taking a history class about the period from 300-1000 CE in western europe. it's our second week and we're currently on the rise of christianity within europe. i just read a statement about ascetics and their actions and i found it really strange (in a fascinating way) the nature to which self-injuring was glorified for the sake of a divine relationship. i know this question veers towards the psychological side, but i've seen questions about the nature of PTSD in the ancient world show up in the FAQ, so i think it's appropriate.
basically, my question is this: to what extent was this sort of behavior different or similar to our modern understanding of self-harm as a coping mechanism? ascetics of the early middle ages starved themselves, whipped themselves, wore hair-shirts, etc. in the name of getting closer to the big G, and this sort of behavior was, on average (at least from my understanding), glorified by the theologian and church theorists around them. how did (if we have enough sources into their psychology) these ascetics feel about the harm they did to themselves? and why was it so popular a movement (in the sense that your average christian regarded ascetics as wise, virtuous people, and not that weird hobo on the outskirts of town that you clutch your toga to yourself when you walk past him)?
And, maybe in a broader sense, how have societal perspectives on self-harm/injury/parasuicide, etc. changed from this stage, where it was okay to harm the self if it was in search of God?
This question might fit better in a subreddit about religion or theology; as mortification (as it is called within Christianity) is something that is still practiced, especially during Easter. Moreover, it is worth noting that practices that you describe about also exist in many other religions, such as Judaism (specially during Yom Kippur), Islam (with their famous fakirs), and Hinduism (for example in Hatha yoga). So I'd suggest a subreddit such as r/Theology or r/AskTheologists.
Regardless, I'll give a short answer (as it might be removed as it is a non-historical question) about mortification in Christianity: The reason for mortification is primarily as a form of spiritual training (as for example Luther discusses in the 26th article of the Augsburg Confession). It is done in order to subdue the will of the flesh, in favor of the will of the soul (as per Gal 5:16). The origin for this is the Bible itself, where it comes up already in the Old Testament (eg Jonah 3:6) and continues into the New Testament where for example John the Baptist wears a hair shirt (Mat 3:4) and Jesus commands that his followers should "take up his cross and follow him" (Mat 16:24). So regarding your specific questions. It is overall rather different from "modern self-harm", as the root for it is not an impulse or a will to cope, but is instead a will to grow. There is probably studies into how practitioners on average feel, but based upon personal experience and people I've talked to about both Christian practices and yoga practices is it a spiritually euphoric feeling (quite similar to the feeling of meditation) as it is just bodily harm but the focus is elsewhere. It was popular, and maintain some popularity, as it has a strong religious/philosophical foundation; which also likely is why it wasn't/isn't rejected by society at large in the places where it is practiced. Finally, regarding your last question so do I have to restate that it still is practiced, just maybe not where you live.