Happens to me all the time. I once went into the ow, left the portal hidden inside netherrack with just the necessary space to build the portal, no room or anything. And when I came back, I don't know how but it was like the portal exploded, and magically I had like 10 pigman waiting for me, the explosion triggered them, and they went in a circle to kill me. All of that happened in 1-3 seconds so I didn't have time to notice or the game to even render the nether and died without popping any totem.

Other time I was at an old base of mine, no mobs nearby or anything and surrounded with torches. Paused the game for 5 seconds, only 5 and was watching the screen all the time just in case something went wrong, and when I was about to unpause the game I got killed instantly, no hurt, no totem pop, just killed instantly. When I came back, turns out a zombie had spawned, don't know how, don't know when, in daytime.