rapid onset pulmonary edema and death. No clue if I am asking that right, but talking about snorkeling after a flight to Hawaii (also wondering about CO2 buildup in a snorkel that is designed to not let water in the snorkel mouthpiece).

Is there any clue to the person snorkeling that something may be wrong? Symptoms to pay attention to if you are snorkeling and come up for just some regular air through your mouth and nose before you get into more trouble?

Trying to understand if it is an overstated risk to float on top of the water with a snorkel, or if I should pay careful attention to how I am feeling?