Extremely frightened.
Could be a reformation of Old English oþ dēaþ ondrǣdan (literally “to be scared to death”).
quake in one's boots
To be very frightened, scared, or nervous.
pack shit
To be scared or frightened.
poop in one's pants
to become extremely frightened.
scared shitless
Very frightened, terrified, scared witless.
matter of life and death
An extremely urgent matter.
scared green
Extremely scared; terrified.