I just read this fact in Hail Mary, but it doesn’t fully add up to me. If you fall flat on your back and wind yourself (phrenospasm) that triggers an immediate suffocation response which has nothing to do with CO2 and seemingly everything to do with a lack of oxygen.

> has nothing to do with CO2 and seemingly everything to do with a lack of oxygen.

If you lack oxygen because you can't breathe in, then CO2 will be building up because you can't breathe out.

Neither sound like a good explaination for the suffocation response being winded causes, because most people can hold their breath for a least a minute with too much discomfort. It's more likely due to a primitive response to unexpected airway restriction - the same as choking.

PS: pigs have the same CO2 response as us, maybe stronger as they can detect C02 at lower concentrations. I find that hard to reconcile with pig abattoirs killing pigs by lowering them into a pit of 90% CO2. N2 would do the same job without the pig realising what is going on, but CO2 is heavier than air so it stays in the pit, making it more economical.

https://pmc.ncbi.nlm.nih.gov/articles/PMC11948533/