I ride bikes and can go for miles slightly running a slight oxygen debt. I swim a lap and stop but have an oxygen debt lower that what I can continue to function with on the bike.
I "think" the trick is simply to turn and continue swimming while maintaining whatever is my current focal point. Tomorrow's focal point is weak side breathing while staying level, not coming up for air and continuing as much forward motion as possible when breathing.
I seem to travel further when not breathing and everything I read points to losing streamline. The answer is ALWAYS streamlining. Whatever takes you off path or sticks out and drags must be put back in line. Simple concept...difficult to implement.