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Perhaps, if one had been active for hours and goes for a swim during the night, would it be possible for the person to fall asleep or get really sleepy?

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In USMC basic training we had to learn the so-called T-Float. It's a survival float where you just hang in the water with your body limp, then every 10 seconds or so you bring your hands up towards your chest, straight out into a T, exhale, and then push down with your hands. You then tilt your head out of the water and inhale. In order to pass, the recruit has to do this for 30 minutes. I did, but fell quite asleep while doing so. They had to wake me up to get me out of the pool. Man, was I relaxed after that!

So yes! You can fall asleep in the water, not necessarily while swimming, as in moving from point A to point B, but you can fall asleep without drowning.

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  • The abnormal breathing pattern must have altered you blood paCO2 and you fell into a stupor. That is not the same as falling asleep. – Centaurus Nov 11 '16 at 0:54
  • It would be pretty difficult to conduct the repeated physical activity necessary to maintain breathing in a t-float while in a stupor. I was there; I fell asleep. Besides, a build up of CO2 in the lungs activates the asphyxiation reflex. That didn't happen. – BillDOe Nov 11 '16 at 6:16
  • I didn't say you were in a stupor while mantaining physical activity. Your abnormal breathing pattern increased PaCO2 (arterial CO2 concentration) and you eventually got into a stupor. That's when someone had to "wake you up". You think you fell asleep. You are entitled to think whatever you like but I doubt a scientist would call it "falling asleep". – Centaurus Nov 11 '16 at 15:09
  • I don't mean to say it's impossible to fall asleep during physical activity. In the medical science very few things can be classified as impossible. However, it's just the there is not a single case described in the medical literature. – Centaurus Nov 11 '16 at 15:16
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    I don't really want to get into a drawn out argument as to whether or not I actually fell asleep on that occasion many years ago. From what I was told I had to be awaken after I didn't get out of the pool after the order to do so was given. I was still continuing the motions involved in the t-float and had been asleep for at least 15 minutes. That would be a very long time to continue motion while in a stupor. And at no time was I gasping for air. I was also told that this was rather rare, though not unheard of. – BillDOe Nov 11 '16 at 20:43

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