You might not notice with adrenaline pumping. As for lethality it really depends on where in your stomach you get hit and the care you get afterwards. In terms of the fight if it’s just your stomach area getting hit nothing shy of a spinal hit would instantly stop you. If they hit an artery you’ve got minutes. If they puncture your intestines and you can’t get care days, before infection catches up to you.
For the actual conflict the only things that will instantly stop are central nervous system hits (brain/spine). Heart and lungs are the next worst, but wouldn’t stop you from claiming a pyrrhic victory. Major arteries are the next big thing to worry about.
The worst part about getting hit in a non vital part of the chest wouldn’t be the force of the blow but the slow agonizing battle with infection that is not unlikely to follow. But absolutely livable and not nearly as bad with modern medical care.