Under The Gun

If I say I am under the gun I mean that there is a threat over me.

And the threat is pretty immediate

so if not careful or diligent or giving proper attention the outcome could be fatal

under the gun is a very strong image

it refers to a very risky situation

it is a serous situation

not just a game

so if it looks like your job is threatened or your health or your marriage or your sanity or the health of your child etc.

that is being under the gun