Back to my point - use the best QNH if there is terrain doubt. If you are over the ocean/etc 1013/2992 will be fine. There is plenty of time (minutes) to change from STD. Re 'Hurtling out of the sky'/bells and whistles - only a temporary problem? By the way, I would NOT wait for 'ATC Clearance'! Just get down - and the chances of hitting something are minimal in reality, and unless you are procedural - in which case ATC can do nothing for other traffic's routing - ATC should notice the rapidly unwinding transponder squawk + the MAYDAY when you can..
It is a big sky and a little feather-ruffling will not cause World war III.