I’ve seen this scenario played out in the movies a few times.
Say your in a swimming pool then all the sudden a baseball comes flying out of the sky and knocks you out cold. Face down in the pool. Would you instinctively hold your breath?
Built in safety feature: Drowning - Wikipedia
You would most likely drown. This is why life-vests are designed to roll you face-up.
While this is true, it doesn’t stop you from inhaling water and drowning. The body’s responses to extremely cold water (so probably irrelevant for a swimming pool, anyhow) make it use less oxygen per minute, but they don’t close the glottis and make you hold your breath. It won’t prevent water from entering the lungs. It will buy you some time for someone to drag you out and get the water *out *of your lungs before you die, but it won’t prevent getting your lungs full of water in the first place.
I am sorry, I am not a doctor. I did not read the paragraph I linked to closely enough.
I believed/assumed that the body naturally stops “breathing” when you go face down in water, and thought wiki confirmed it.
Looking at it more closely, it only mentions heart rate and blood flow. Thanks for the correction.
Read the article again WhyNot:
So if you get to the guy quickly enough before the water enters the lungs your chances of saving him are much improved. This is what must have happened to me at age 9, when I got caught in a runout in Puerto Rico. I lost consciousness somewhere along the way; when some surfer kids rescued me on their surfboard, I awoke right before they got to shore, and I don’t recall coughing up much water if at all.
Ah, thanks! So yes, I was inaccurate to state that there’s no glottis closing; it does close. But it opens again to let water in, 80-90% of the time.
No. Quite the opposite – the instinct is to breathe. You continue to breathe when asleep, unconscious, or in a coma. When your body senses a lack of oxygen, it triggers the breathing reflex, and does so faster as the lack of oxygen gets worse. Which is a bad thing, when your face is underwater – often fatal.
No, because breathing is the instinctive reaction. Holding your breath is a conscious decision.
Did posters #8 and #9 read posts #6 and #7? Are you explicitly disagreeing with John DiFool at #6, or did you just not bother to read the rest of the thread?
Not disagreeing at all. Post #6 doesn’t state that one doesn’t breathe, only that the spasms allow for a greater chance of a successful intervention if someone arrives early in the event. As post #7 pointed out, the vast, vast majority of the time, water is allowed to enter the lungs.
A throat spasm is NOT holding your breath. There’s nothing in what I said that was contradicted by those two posts. Reading is worthless if you don’t have comprehension of what you read, as well.
not a doctor or para but i’ve known people who (i guess they’re lucky) got concussed but fell into a body of water. the water hitting your sinuses and larynx are all you need to wake up from the concussion. however, one seriously knocked guy sank straight to the bottom.
I’m not a doctor or otherwise medically trained, by a semi-experienced SCUBA diver, so I do have some knowledge regarding the body’s reaction to being under water.
The reflex to breath is extremely powerful, and can’t be overcome even consciously. Don’t believe me? Try holding your breath until you black out, it can’t be done. This reflex is triggered by the presence of carbolic acid in the blood stream, itself originating from the carbon dioxide which isn’t being expelled by the lungs.
Likewise, this reflex would force even an unconscious person to breathe in a lung full of water, i.e. drowning.
The mammalian diving reflex has little effect in this situation. It allows you to hold your breath longer under water, but it won’t stop you from inhaling it. It has on occasion saved the lives of SCUBA accident victims, where the damage from oxygen depravation was minimized due to their decreased metabolisms.
Wha? Thats exactly what it is. Blocking the airways using nothing but one’s own muscles is the very definition of “holding one’s breath.” And as the article says, some people’s bodies will do this to the point of suffocation.
And that’s pretty much the answer to the thread. In the immediate aftermath of being knocked out and face down in a pool you’re likely to hold your breath. Water hitting the wind pipe causes layrngospasmic reflex and prevents inhalation.
Whether this persists indefinitely is a moot point as one way or another, if the situation is not remedied, you’re going to suffocate.
In summary, you know a lot of “lucky” people who got concussed and fell into a body of water? 
You have an odd definition of lucky!
PS. Who grabbed the guy who sank to the bottom (and… bottom of what?)
actually a whopping two. one guy was drunk by a pool and a bunch of half-wits elbowed him (in the head while standing upright.) he toppled into the deep end and sank like a rock. when fished out, he didn’t need CPR. said he wasn’t conscious falling but woke up sinking. the other guy fell into a drainage sump he was excavating but some of the rocks slabbed off the sides and he fell. the water at the bottom wasn’t deep, just chest level, but he says he blacked out from the impact and woke up from the feel of the water.