There's a theory that Bakugou's anger and constant adrenaline is his body's way of dealing with his quirk and keeping him alive. Because nitroglycerin can lower a person's heart rate dramatically, so if he's not constantly stressed he would literally pass out. Which would kinda make sense because he only started being so angry all the time after his quirk manifested.
BUT
nitroglycerin is sometimes used in medicine for chest pain and prevention of heart attack, it also improves blood flow through the heart. So if Katsuki’s body produces nitroglycerin, it only makes sense that his body wouldn't get affected by it, but instead, he will only get affected by the force of his quirk since nitroglycerin is used for explosion. I mean imagined mini explosion happening in your hands, and all the pressure in your limbs are something your body even Katsuki can't handle for long. And also he has been producing it for 11 yrs! He would be dead because Katsuki also sleeps which is a way to calm down and lower his heartbeat Also for it to effect his heart it would have to be in his blood but the nitroglycerin isn’t in his blood, it’s in his Excretory system which involves the dumping of waste (pooping, peeing, sweating, sneezing, coughing, and throwing up)
so no...Scientifically speaking he isnt going to die if he calms down.