We do actually have the Jesus prayer, or variants of it under the category called ejaculatory prayer.
http://www.catholictreasury.info/books/devout_life/dev36.php
goes over them
Do not trust in me, my Jesus, because I shall never do any good.
I distrust myself, but I trust in Thee, my Jesus.
Eternal Father, for the love of Jesus Christ have pity on me. My God, I wish for Thee alone, and nothing more.
Send me any Chastisement, but deprive me not of the power of loving Thee. I thank Thee that Thou gives me time to love Thee. I love Thee, my Jesus, I love Thee; and I hope to die repeating, "I love Thee, I love Thee."
'I give You my will, my liberty; dispose of me as You please.'
'Thou art omnipotent; make me a Saint.'
'May I die rather than ever offend Thee again.'
'O God of love, give me love.'
are some examples
Another my favorite saint was fond of was begging not to be sent to hell
>>789665
The discipline is a reference to the tool, that's what it's called,
others included chains on legs which caused pain or things which restricted movement, hair shirts that were itchy/uncomfortable, things with eating like adding bitter liquid or ashes, or just cold showers.
There are many reasons it's done, to become detached from the world/pleasures, gain better control over your body, offer the suffering to Christ so that he can help others, become more united to Christ by the suffering and a couple other things.
It's really only reserved for people quite advanced in the spiritual life usually at monasterys though. A key part of it is absolute obedience to one's confessor, if they instruct you to alter or stop you must follow.
This nature of mine," she used to say, "inside and out is always seeking its satisfactions, and always on the lookout for a respite. Give me leave to do all I can to overcome self. The flesh would like to command, and instead I wish to make it serve me as it ought, now and forever."
Look Jesus, it is my body that rebels, but I shall know well how to manage it. It often cries out, and would fain not obey me, but I'll see to that. Yesterday it seemed as if it would revolt, and I made it keep quiet by dint of hard blows.
Some quotes from a saint on it
We view sin as incredibly evil/bad and it makes sense to make steps to avoid it
Basically every saint or atleast some of the greatest ones practiced it devoutly
"To defend his purity, St. Francis of Assisi rolled in the snow, St. Benedict threw himself into a thorn bush, St. Bernard plunged into an icy pond… You… what have you done?" […] "If you realize that your body is your enemy, and an enemy of God's glory since it is an enemy of your sanctification, why do you treat it so softly?"
"If we are cruel in crucifying the flesh, you by sparing it are far more cruel."
And again to be clear to anyone reading this, do not do anything without explicit permission from your confessor/spiritual director