The term running amok was originally used in the 19th century to describe the strange behavior that sometimes affected Indonesian natives. Far from the whimsical connotation the term has today, running amok originally involved a man, overcome with rage, grabbing the first weapon he could, and rushing through the streets, killing everyone he could. As many as twenty people could die in this situation, before the madman was finally killed - a man amok would never let himself be taken alive, always fighting to the death.
It is unclear what caused these insane fits of rage, but it was common for the killer to be someone who had just experienced a great personal loss or was otherwise pushed to the point of desperation. One theory is that running amok was a form of suicide, like the Japanese seppuku, only in this case the goal was to take as many people as possible with you.
Unfortunately, it seems that running amok has continued in spirit, if not in name and seems to be happening with increased frequency in recent years.