means a sudden, overwhelming surge of fear or anxiety that overrides clear thinking, often spreading quickly through a group or market.

from From the Greek god Pan, the goat-legged deity of wild places, whose eerie cry in lonely woods and mountains was blamed for the inexplicable terror that could seize travelers and flocks. The Greeks called this sudden dread panikon, 'of Pan,' and it traveled through French (panique) into English. So the word literally means the kind of fear a forest god gives you — irrational, contagious, and seemingly out of nowhere.