How do noid overdoses kill people?

I have experience smoking powdered noids off of foil and have felt like I was dying in a couple of those instances. I’m curious as to how these chemicals could actually kill someone. Like what does it do to the brain that would cause the body to shut down?

I think complications from seizures. Also found this which seems to indicate that vasoconstriction can prevent blood flow to key areas of the body and cause death.