If you are drowning and magically healed do you drop to 0 at the start of your turn or get all your breath back? @JeremyECrawford
— Thomas Gaia (@Critter_from_Oz) December 2, 2016
As of the PH errata, you can't regain hit points if you've run out of breath and are at 0 hit points: https://t.co/vzc7twThef #DnD https://t.co/fibafkIw5i
— Jeremy Crawford (@JeremyECrawford) December 4, 2016