WDB FLC ALLOWS AIRSPD TO DETERIORATE BELOW FLAP SETTING SPD. ABRUPT PWR INCREASE; PAX NEED MEDICAL ATTN.

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I WAS FLYING FROM FRANKFURT; GERMANY; TO IAD. WE HAD BEEN AIRBORNE APPROX 8 HRS. WE WERE UNDER DULLES APCH. DUE TO AREA TFC CONGESTION WE WERE GIVEN NUMEROUS ALT; HDG; AND AIRSPD CHANGES FOR SEQUENCING. I WAS USING THE AUTOPLT AND AUTOFLT PANEL TO MAINTAIN SPDS; ALTS; HDG; DSCNTS. PLUS I HAD TO FLAP CONFIGURE; CLEAN UP FLAPS AND RECONFIGURE DURING OUR MANEUVERING. ON DOWNWIND; WE WERE SLOWED AND I WAS SETTING UP THE AUTOFLT PANEL TO USE THE AUTOPLT AND AUTO THROTTLES. IN DOING SO; I THOUGHT THAT ALL WAS SET AND WAS LOOKING OUT FOR ATC TA'S. FOR WHATEVER REASON; I DID NOT NOTICE THE AIRSPD GO BELOW THE FLAP SETTING FOR 170 KTS. AT APPROX 145 KTS MY SCAN CAUGHT THE AIRSPD BEING LOW. I IMMEDIATELY APPLIED FULL PWR; KICKED OFF AUTOPLT AND NOTICED THAT DURING MY QUICK RECOVERY THAT NO AUTOTHROTTLE ALERT LIGHT OR FLAG WAS DISPLAYED. THE POINT IS THAT; IF I DID ATTEMPT TO LATCH THE AUTOTHROTTLES; THAT I DID NOT VERIFY SO; AS I HAD DONE SEVERAL TIMES PRIOR DURING THIS APCH PHASE. ALT CHANGE WAS MINIMAL; APPROX PLUS 15 FT AND I QUICKLY HAND FLEW IT BACK TO OUR ASSIGNED. AS FAR AS CAN BE DETERMINED; THERE WAS NO OTHER DISCREPANCY OTHER THAN THE 150 FT GAIN. THE ACFT WAS WELL ABOVE STALL SPD; NO STICK SHAKER WARNING. STRAIGHT AND LEVEL. MY INDICATION THAT SOMETHING WAS NOT CORRECT WAS THE INCREASED NOSE-UP ATTITUDE WHICH PROMPTED MY IMMEDIATE APPLICATION OF PWR. IN SUMMARY; DURING THE NUMEROUS ACFT HDG; ALT; FLAP; AIRSPD CHANGES IN A BUSY ATC ENVIRONMENT INCLUDING THE FATIGUE OF AN 8 HR FLT; THAT THE DISTR WAS MY SCAN ON THE AUTOFLT PANEL DID NOT VERIFY THAT WHEN AN ATTEMPT WAS MADE TO LATCH THE AUTOTHROTTLES; THAT INDEED THEY WERE ARMED AND OPERATING. IN ADDITION; WITH A GREAT AMOUNT OF PWR BEING APPLIED SUDDENLY THIS CAN RESULT IN SOME UNCOMFORTABLE FEELINGS TO SOME PAX DUE TO THE INCREASE IN NOISE AND ACCELERATION WHEN THEY ARE EXPECTING A LNDG. 2 PAX NEEDED PARAMEDIC ATTN UPON LNDG; ONE FOR AN APPARENT SEIZURE; ETC; AND THE OTHER UNKNOWN. IT WAS HEARD BUT NOT CONFIRMED THAT THEY WERE RELEASED APPROX 30 MINS AFTER BEING DEPLANED; AND AS CAN HAPPEN; THIS CAN TRIGGER SOME REACTIONS AMONG CERTAIN FLYERS. ALTHOUGH THIS RPT DOES NOT IDENT AVIATION SYS PROBS; IT DOES REFLECT THE POSSIBLE EFFECTS OF NUMEROUS AUTOFLT INPUTS IN A SHORT PERIOD OF TIME IN A BUSY ATC ENVIRONMENT AFTER A LONG TRANSATLANTIC XING EVEN WHEN IT APPEARS ALL IS GOING SMOOTHLY.