It feels obvious, but, how do something stopping existence cause signals rising? Do they have molecular scale system heartbeat monitoring, or what? I don’t see data to draw conclusions from.
My understanding is that it stops oxygen uptake from your blood to your cells, so it feels like you're not getting enough air, like you're choking or drowning. But I'm not an expert.
I've accidentally passed out from breathing helium from a 10-foot weather balloon. It's not painful at all, actually slightly pleasant. A lack of oxygen absorption doesn't directly cause discomfort.
Increased blood CO2 is the main cause of discomfort from holding your breath for a long time. This is why hyperventilating to bring your CO2 level down helps you hold your breath longer. (The light headedness from hyperventilation is a consequence of low CO2.)
I don't believe cyanide particularly increases blood CO2 prior to loss of consciousness. Also, I'm told carbon monoxide poisoning isn't particularly uncomfortable, and also interferes with oxygen transport. So, your proposed mechanism seems unlikely.
Someone else here mentioned that cyanide poisoning is painful due to lactate production: that muscle burn from working out, but presumably worse, building until death.
Other tissues besides muscles may also have lactate receptors; I'm not sure. If that's the case, your whole body may have that workout burn.
This is such a jordan peterson style non-answer x 'what does it really mean to order a pizza"