It makes sense that if you inhale massive quantities of glycerin aerosols, some of it will deposit in throat, trachea, lungs. Some will be absorbed, some will just thicken natural secretions that are coughed up as phlegm. It's perfectly natural, and the fact glycerin is completely soluble in water makes it disappear if you're adequately hydrated. I think the "heaviness" is when the amount of glycerin in secretions gets above a certain percentage. If i vape incredibly heavily, it's very noticeable. A hot shower with the steam loosens it up well. Frankly, I'm less worried about that than just about anything in our environment. If it's ever suggested that breathing glycerin mist causes metabolic changes that are harmful, I'll certainly consider the evidence carefully. Having switched to all-glycerin, i find I really notice the effects of different flavorings, how some are more cloying, others harsh, etc. I stick to what i can chain vape and doesn't make me feel tox'ed. It's going to be pretty subjective, once the main offenders like PG are down from 50-70% to tiny percentages.
For instance those "use at 2.5%" sper-concentrated Chinese alcohol-based flavorings just feel bad to me, i can't really say why, and I'm not sure if it's all of them, but i can't find a way to blend them that doesn't char my throat and lets me wake up feeling reasonably clear-lunged. I don't think it has anything to do with the minute amounts of alcohol. Maybe they use diketones, maybe it's that sweetener they use, no idea, and i hate to waste 12 bottles of flavoring, and the flavors are clever, but, drat, my body's telling me to skip 'em.
Another detail. Some people vape lightly, the way you'd smoke a few cigs a day, and they can go with high nicotine liquids, drenched in PG and flavored to the gills if they like that. But for those of use who REALLY vape, it's a more critical issue.
