As in, "to be under fire lock." A word used to describe a person who is experiencing the momentary stun one feels at the first blare of a fire alarm.
Seriously, how are you supposed to act calm in an emergency when you seize up and start bleeding from your ears?
*Someone blows out a match in the storeroom, fire alarm sounds*
"Holy shit! I think Jim's heart just stopped!"
*covering ears* "Nah bro, that fuckin' fire alarm just put him under fire lock."