In the Catholic tradition of spiritual growth, “mortifications” refers to (unenjoyable) practices by which we can unite ourselves to the sufferings of Christ. Fasting from food or from certain kinds of food would be examples of this, or kneeling for extended periods in prayer.
Hunger for exterior mortifications can be a good thing, and the absence of such hunger is probably a sign of a problem in a Christian’s spiritual life. Even if we aren’t always engaged in those practices, it is no doubt healthy to be inspired to engage in them.
When inspired to do so, I would say, do practice exterior mortifications, but cautiously. Be careful about doing too much, which can be spiritually harmful (and in some cases may even do damage to health or relationships or to others). It’s better to start by erring on the side of doing too little at first, and then to add more later when ready.
We very often forget this, but it is valuable to try to make exterior mortifications secret, not even letting one hand know what the other is doing, so to speak. Keep it between oneself and God. If the mortifications are much harder to sustain when they’re secret, that tells us something about our motives. If they aren’t hard to sustain, then we should all the more continue to keep them hidden, a secret for oneself and God.
Some mortifications are difficult to do secretly with others around, but it is valuable to find a way to mortify ourselves even then, because that is when we are most tempted to pride or malice. The mortifications best suited for the company of others, indeed which draw their terrible power precisely from the presence of others, are interior mortifications. Rather than accepting bodily pain, interior mortifications accept mental or emotional pain. When someone speaks unkindly, accept it without complaint. When someone accuses falsely, accept it without protest.
It seems that it is hard to overdo interior mortifications. There is endless opportunity to practice them, and somehow failure to do well doesn’t bring a sense of shame and discouragement in the same way that failure in exterior mortifications can.
The person who continually seeks to practice interior mortifications is a meek and humble person (which is not to say a weak person). These people have unseen depths beneath the surface. Their silences have more power than most people’s words. They are in truth unbreakable, immovable, unconquerable, no matter how they might first appear from the outside.