I'm synthesizing here, but AFAICT a catatonic-like state is typical of small children in severe distress. (Anybody remember the Moth Radio Hour story about the man whose kid immediately went catatonic when they were surprised by burglars? IIRC, he was told this response was common of young children.) So if a baby suddenly inhales a large amount of water, they may immediately go from normal to non-responsive (possibly retaining muscle tone?), even though they're not yet physiologically drowning, and even though with lesser amounts of water they would normally cough and cry. This [lack of] behavior may be related, if indirectly, to the phenomenon of SIDS. An infant's physiology hasn't developed the various mechanisms to jump start respiration when something goes awry. (One unproven hypothesis behind SIDS is that an infant's breathing is partly moderated and even induced by their caretaker's breathing, such that if they can't hear, feel, or otherwise sense--some theories implicate carbon dioxide levels--another's breathing their own rhythm may be disrupted, or if disrupted less likely to resume. Thus co-sleeping may be better for infants, reducing SIDS risk, ceteris paribus--i.e. absent counter-indications, such as a parent who smokes or drinks.)
So with babies not only do you have to watch them to make sure they aren't presently, visibly drowning, you have to make sure (to some reasonable, mentally healthy degree) they couldn't possibly be drowning--i.e. they didn't or couldn't have inhaled water; that they're active, attentive, etc.
We attended an infant cpr class via zoom, learned nothing. We at least got the message about SIDS, but the lack of tribal knowledge in the first six weeks was pretty brutal as first-time parents.
For my third, they made us watch a series of videos on a range of topics over about 2 hours, which made me think "Yes, of course, this should be the absolute minimum required for a new parent".
We had great parenting lessons, and more importantly, got a phone number "if you have any question or problem, call us".
My wife had a problem breastfeeding: it hurt her, a lot. She asked the nurse what to do, and the nurse was like "dunno, happens to many mothers, use a formula if the problem persists". We used that phone number instead, a lady came to us "show me how you feed the baby... ah, I see, the baby is under a wrong angle, here is how you should do it instead". Problem solved. Lucky us, but less lucky all the mothers who asked the same nurse, received the same answer, and didn't have a friend on the phone. (It also makes me wonder about the utter lack of curiosity with some people. Like, the nurse probably keeps getting the same question regularly for years, and she can't even, dunno, use google, or ask a colleague?)
I recommend trying a child carrier with a little baby. Not the giant type where you wear a huge metallic construction with the seat for the baby, but the ones made from cloth, where your child is on your body, vertically, facing you. -- You can walk around your house, carrying your child with you, and both of your hands are free. You can walk outside in winter, and don't have to worry whether your child is sufficiently dressed. You feel your child's heatbeat and breath, so you don't worry about SIDS. When the child doesn't want to sleep, you can take a walk outside, and maybe read a book. (Then the tricky part is removing the child from the carrier without waking it up. I learned to lay down on my back, unfasten and open the carrier, roll over and leave the child on the bed; still only about 50% success rate.)