I had a player fighting against sahuagin by the shore the other day and he was dropped to 0 and dying. Because of his location, though, he landed in shallow water (2-3' deep) which I ruled was enough to drown in.
The rules for suffocation (PHB pg. 183) are specific to state:
A creature can hold its breath for a number of minutes equal to 1 + its Constitution modifier (minimum of 30 seconds). When a creature runs out of breath, it can survive for a number of rounds equal to its Constitution modifier (minimum 1 round). At the start of its next turn, it drops to 0 hit points and is dying.
I was having difficulty adjudicating this because the character was already at 0 and now was just inhaling water.
In this scenario, does the character just make death saves as normal, or would they automatically fail them?
FYI, I ruled that he would auto-fail the saves since he's just inhaling salt water now and takes a level of exhaustion, but if the rules have something specific for this, it'd be helpful to know.