Now I will say that 5th edition feels less safe than 4th edition but just not enough to give us that sense of danger and loss.
4e was tricky at higher levels because fights went on for so many rounds which made for so many chances for things to go horribly wrong.
I generally found 4e a little to the easy side of challenging across levels. Tiers had a sort of shock value. When you first played Paragon, the sudden increase in out-of-turn actions could feel a little crazy, but once you got used to it, the overall challenge stayed fairly even across levels, as long as you faced 'level appropriate' challenges, which could vary considerably if you were playing the sandbox style...
5e fights are so short - most of ours are done within 3 rounds and at low levels somebody in our party gets knocked down. This makes it brutal and captures the feel of pre 3e - but only at low levels.
Yep. But that was, IMHX, the feel of pre-3e, specifically AD&D. At low level, randomly deadly to grindy. Fun/challenging through the 'sweet spot' of mid levels. 'Too easy' (not exactly, more like made challenging only by increasingly insane 'gotchyas,' leading to rampant paranoia) at high levels.
Aside from cutting down the hit dice as others have suggested, I would restrict the 3rd level spell Revivify because it does undermine lethality, or just ramp up the monsters and drawn those fights out.
You can always make 5e deadly by throwing enough monsters at the party, assuming they can stand up to the party's AE capacity (whether through toughness or good tactics), thanks to bounded accuracy.
I actually liked the addition of Revivify in 3e (I think it was 3e, that was when I noticed it, anyway). To me it comes off as dramatic life-saving, while actual Raising seems to cheapen death.
Did you play the same AD&D as everyone else lol? Save or die dude. You didn't grow out of that. ...
Sometimes I wonder.
Mostly I think I just didn't forget as much of it.
For instance, you absolutely did 'grow out of' SoDs in 1e. At high level, "save: neg" started to mean 'does nothing.'
"SoD" only became the win (or lose) button (and the acronym) when 3e gave everyone 'bad' saves that stayed bad no matter what level you got to and let you powergame untouchable save DCs. That's something D&D never recovered from. In 4e, you'd have a Non-AC defense or two that couldn't keep up with the treadmill, and in 5e most classes have 4 bad saves.
That's another thing you could do if you want more dead PCs, Corpsetaker, introduce some SoDs.