That's basically what the mod does.
If for some reason your head ended up inside a solid full cube block like sand, gravel, dirt, stone, etc. you start to lose breath. If you run out of breath while still inside, you lose 10 HP (or 5 “hearts”) per 2 seconds, so it is very deadly. On the other hand, losing breath is always rather slow in Minetest, so you have plenty of time to escape.
Specifically, suffocation will be added to all blocks which:
- Are solid
- Are full-sized standard cubes
- Don't already have their own forms of damage
- Are not excluded from suffcation by mods
GIt project page: http://repo.or.cz/minetest_real_suffocation.git
Works in Minetest 0.4.16 or later
License of everything: WTFPL