Why do I begin to feel good when hit hard?

Occasionally, while fighting, my character "begin[s] to feel good when hit hard." What does this mean? I've tried searching the wikia for the phrase, but I can't seem to find it.

Solution 1:

It is flavor text that means that your Constitution score has gone up by one point. Usually because a number of things such as using Constitution-based skills or eating certain kinds of foods. Of note, Medium Armor and Heavy Armor are CON skills that train simply by wearing that armor and moving around, while Polearms and Staves and Blunt all train just by attacking. But perhaps more to point - Healing, which is your natural recovery, trains any time you heal up. So Constitution tends to train pretty well in the background as a result, for any character.