Being in Florida the water is probably not going to be that cold, but my recollection of an event quite a few years ago may relate to how this man died.
Some Japanese exchange students were playing soccer beside the Aire River in winter. The ball went into the river and two students jumped in to retrieve it. Both apparently went straight under and drowned. The water in this case was very cold, say 10 degrees.
"... In humans, cold shock response is perhaps the most common cause of death from immersion in very cold water, such as by falling through thin ice. The cold water can cause heart attack (as cold blood from the extremities reaches the heart) and inhalation of water (and thus drowning) from hyperventilation...... "
en.wikipedia.org/wiki/Cold_shock_responseWhether you can swim or not, this is something to be aware of, especially if teaching non-surfers to SUP in cold water.