WTH? I've experienced my share of "This is not a drill" when Soviet subs got to close. Never had a nightmare, but it does get the adrenaline flowing unlike a General Quarters, "this is a drill." You still have to hustle just as fast through the passageways and ladders to get to your assigned General Quarters. It's like an orchestrated cluster-frig with the entire crew running in all directions. It was kinda funny at times.
On one of the submarines on which I served we used to stand amidships for General Quarters and shout, “Everyone aft, go forward! Everyone forward, go aft! Everyone amidships, direct traffic! ;-)