Recently I noticed that in the nether (may happen elsewhere, I am not sure), if I was near lava (but not immersed in it, and it could happen through a 1-block wall) , I would rapidly take damage (but not catch on fire). It happened several times in several locations, and in cases where the lava happened through a wall, filling in the source block (which removed the lava) ended the damage source.

I was streaming on Twitch at the time, happened at 7:46, 13:25, 13:34 in this video:
https://www.twitch.tv/videos/1210432883

I am not using any packs that change game rules.