Suffocation

Suffocation is when a player is unable to breathe due to his upper-half being inside of a block. This is very common when two or more blocks of sand or gravel fall on the player. Suffocation deals 1/2 a heart of damage every .5 seconds, which is the same damage as received while drowning, but twice as often. Vision also blurs during suffocation.

You can also suffocate if you try to get into a minecart with only two blocks of vertical room - as the minecart will take the bottom, your feet the middle and then your head will be stuck in the block above you.

Attempting to suffocate yourself in Indev, Survival or Creative will not cause any harm to you.