Lots of damage from a under-water chest

Put the summary of the bug you're having here

What I expected to happen was...:
I Swam into a boat to open a chest, expecting it to open

What actually happened was...:
The chest didn't open, I went up for air then came back to the chest, when the chest opened I went down to one heart for apparently no reason.

Steps to Reproduce:
Here is the clip of what happened: https://clips.twitch.tv/AbstemiousRefinedMonkeyPeoplesChamp-gynMCU9sjWdqEYqn