We see this all the time here in the accident reports involving snorkeling and diving. In nearly all instances it involves people of "age". They either have pre existing medical conditions, their unfit, overweight , unskilled or all of the above. If you're not fit to be in the water, don't put yourself and others at risk.
“Cardiac issues are now a leading factor in diving fatalities,” said
study author and diver Dr Peter Buzzacott, of the University of Western
Australia. Divers who learned to dive years ago and who are now
old and overweight, with high blood pressure and high cholesterol, are
at increased risk of dying.”
Cardiac events now come second only to drowning as a cause of death among divers.