I can hold my breath for 30 seconds. If I know it's going to happen I'll prepare with a full lung.
I assume I won't be sent to something like the marianas trench where the pressure either coming or going would kill me, and since after the 30 seconds I'll be dry even if I mess up and take in some seawater worst case it will be a terrible few minutes of gasping when I'm back.
Edit: I have no idea how "I won't be sent to", got turned into "intelligent" by autocorrect.