B757 FLT CREW EXECUTES A GAR WITH THE ACFT BECOMING UNSTABILIZED IN AN UNUSUAL ATTITUDE.

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AT MINIMUMS I CALLED NO RWY/ENVIRONMENT AND CALLED FOR THE GAR. THE PF INITIATED THE GAR BY PUSHING THE TOGGLES AND DISCONNECTED THE AUTOPLT. I BACKED HIM UP BY CALLING FOR FLAPS 20 DEGS; HE AGREED. I LOOKED DOWN TO THE FLAP HANDLE AND POSITIONED THE FLAPS TO 20 DEGS. WHEN I LOOKED UP THE ACFT WAS IN A 25+ DEG BANK AND THE NOSE WAS DSNDING THROUGH THE HORIZON. THE FLT DIRECTOR WAS FULL NOSE UP AS I TOOK THE ACFT TO PULL UP AND GO WINGS LEVEL. THE PWR WAS AT MAX THRUST AND THE AIRSPD WAS INCREASING RAPIDLY. THE ACFT WAS SOMEWHAT STABILIZED AS THE PF TOOK THE ACFT BACK; SOME OSCILLATIONS FOLLOWED THAT INCLUDED A 'DONT SINK' CALL FROM THE EGPWS. I TOOK THE ACFT ONCE AGAIN AND STABILIZED IT. IT ALL HAPPENED SO FAST THAT I CAN'T BE SURE ABOUT ALTS; PITCH AND BANK BUT IN RETROSPECT I HAVE WITNESSED THIS EXACT SCENARIO; IN THE SIMULATOR. THE LOW VISIBILITY APCH CONVERSATION DID NOT TAKE PLACE. EVEN IF WE WERE NOT CONDUCTING A CAT 2 AND OR 3 APCH THE BRIEFING GUIDE CERTAINLY LENDS ITSELF TO THOUGHTFUL CONSIDERATION OF THE EXACT JOB OF EVERYONE INVOLVED INCLUDING THE AUTOPLT. THE AUTOPLT WAS DISENGAGED AT THE WORST TIME.