That unnerving feeling when
something has gone horribly wrong while doing
work and your anus tightens up in a flinching and constipated way. It's a form of panic attack when you realise your life / career just ended and you
go into a wild panic to try rectify the situation before you get found out.
Boss: While you're updating all the systems, if it goes pear shaped, don't have a nipsy twitch, just get it fixed!
or
Worker: I
hit the red button instead of the green
one and suddenly felt my nipsy twitch.