There is no such thing as negative HP in 5th Edition D&D, correct.
Its essentially whenever the damage = current HP + max HP.
I'm a bit curious, do you often play with medium encounters? Prefer using average damage? Never play with low HP PC's?
I'm trying to imagine a playstyle where this doesn't show up at least once in a typical 1-10 campaign.
I have a tendency to run hard encounters, in part because adventure and real time pacing makes it tricky to run 6-8 encounters in a game day. I roll damage, but the PCs did get a slight HP buff in the game I was running for about a year and a half (it's on hiatus at the moment; hoping to resume next year). The PCs had recently hit 8th level when we went on hiatus, as I run relatively slow advancement.
To detail the HP buff, since it seems to be the most relevant data point for your survey, I let them always take the top half of the die if they roll lower. So, for example, a Fighter gets to roll their D10, and if it's lower than a 6, she gets a 6. This was very useful for them with the difficulty of fights I was throwing at them, especially in the first few levels, though I'm regretting it a little now.
No one's died from massive damage yet. The only PC death was one which got polymorphed into a weasel by some malevolent pixies, then swallowed by a Giant Frog. He failed one death save, then rolled a natural 1 on the second save before another PC got to him.
I've had, I think, three fights over the course of the campaign which were so nasty that they nearly wound up being TPKs, but in each instance, one or two PCs held on conscious and fighting (actually in one of them, the Fighter made two natural 20 death saves to stand up and resume fighting) until the end, and were able to stabilize and heal the rest.
For most of the campaign I did not have enemies specifically target downed PCs (though they occasionally got caught in the AoE of damaging spells), though I started to change that later in the game. Had an evil angel specifically coup de grace the Fighter and kill her in front of her best friend in one of their last fights, but said best friend was a cleric with Revivify, so that was temporary.
