How can a snakebite victim die faster if he is hopeless, scared and terrified than if he is calm?

The most glaring and obvious effect of being scared or terrified when one has been bitten by a poisonous snake is that, when you are scared, your heart rate increases and your blood pumps faster.  This is what is supposed to happen because we get scared when there is danger to our safety, and we need extra oxygen to fight or flee.  This is how humans have survived since the beginning.

In this case, though, that works against you, as the faster your blood pumps, the faster the poisonous venom from the snake reaches the heart and the brain, whereas a person who is calm has a slower pulse, and more time before the bite becomes fatal, and therefore more chance to get help and survive.