If you've already googled tonight, you've met the term "dry drowning," and it's probably why you're still reading. So here's the honest version.
The viral idea is that a child can be perfectly fine, go to sleep, and silently drown a few hours later from a swallowed sip is not how it works.
Doctors, including the team at Penn Medicine, have pushed back on the term itself. Real breathing problems after a bath are rare. They happen when water goes down the wrong pipe, into the airway, not when it's swallowed into the stomach.
And when they do happen, you can see them: constant coughing, hard or noisy breathing, unusual tiredness. They don't show up out of nowhere in a baby who seems fine.
Swallowing goes to the stomach. Trouble comes from the airway, and the airway complains loudly. A baby who finished the bath happy and is breathing normally is not silently in danger, and you don't need to stay up all night watching them sleep. Watch for the symptoms above for the rest of the evening, and let yourself relax if they don't show.