When ascending from water quickly with a block over the water with a space in the middle and a block in front of you just out of the water, you jump into the block overhead and get pushed out causing half a heart of suffocation damage. This is likely a glitch with the mechanic in which you automatically ground jump when close to a wall in the water mixed with the reduced height of the character while swimming fast with the momentum pushing you up. You jump as you exit full swim and clip the ceiling.