Why paracetamol iv can cause sudden death?

It does not: However, too much paracetamol (acetaminophen, "tylenol") will destroy the liver and cause death in a few days. This is common. There is one very famous case in which a beginning physician foolishly prescribed intravenous paracetamol in a dose similar to what one would take by mouth, and this led to a death. Don't exceed recommended dose by any route.

Overdose: Other than an overdose I am not sure that death is a significant risk.