I hadn’t—until I saw this scary report from ABC News about a 60-year-old man from Yonkers, New York, who fell into the Long Island Sound from a friend’s boat, pulled himself out of the water, and then died a few hours later from … drowning.

How is this possible? It’s shocking, and experts say it’s pretty rare, but here’s what happens: When people almost drown, they swallow a significant amount of water, which enters the lungs and interferes with their ability to circulate oxygen and remove carbon dioxide. Death by asphyxiation occurs one to 48 hours later.

Imagining my own toddler swallowing his fair share of pool water during our weekly swim lessons, I quickly Googled for more information. Here’s what I dug up: Although delayed drowning symptoms can be hard to detect, NYU pediatrician Daniel Rauch told The Today Show that three important signs include difficulty breathing, extreme tiredness, and changes in behavior after the incident; all can indicate reduced oxygen flow to the brain.

An emergency medicine doctor told ABC News that anyone who experiences a near-drowning experience should be checked out in an emergency department and possibly observed for 24 hours. The good news: Experts agree that delayed drowning is survivable with fast-enough medical care.

I know these incidents are not very common, but it’s another important reason to stay alert around water—especially if you’re with young kids, who are prone to swallowing water, and older adults, who may have underlying health issues that can exacerbate the problem (as may have been the case for Tommy Mollo, the aforementioned Yonkers man).

And as I learned in this Reader’s Digest article from last summer, drowning isn’t always what you think it looks like.

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