Cyanide inhibits cellular respiration. It prevents your body's cells from using the oxygen in your blood to produce energy.
My understanding (I am not an expert, please feel free to correct me) is that this produces neurological signals that you're not getting enough air. So you feel like you're choking or drowning; you're gasping for breath, your whole body is screaming at you that you need to breathe, but you are breathing and it doesn't help. That's not a pleasant way to go.
According to my biology teacher, the urge to breathe is from receptors that detect a higher concentration of carbon dioxide (in blood I suppose), not an absence of oxygen. She also said if you placed cyanide in your mouth, it would kill on contact with the tongue, before you managed to swallow it.
Your biology teacher might have been correct, but I had a science teacher confidently tell my class (in an affluent, otherwise science-respecting school) that humans don't land on the dark side of the moon because they would float away due to gravity working the other direction (hence the name).
Cyanide inhibits cellular respiration. It prevents your body's cells from using the oxygen in your blood to produce energy.
My understanding (I am not an expert, please feel free to correct me) is that this produces neurological signals that you're not getting enough air. So you feel like you're choking or drowning; you're gasping for breath, your whole body is screaming at you that you need to breathe, but you are breathing and it doesn't help. That's not a pleasant way to go.