AN ACR B737-200 CLBED IN A HOLDING PATTERN WHEN THE ALT HOLD APPARENTLY WAS DISENGAGED.

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ESTABLISHED IN HOLDING PATTERN FL250. MY FIRST FLT ATTENDANT ENTERED THE COCKPIT WITH A FORWARD GALLEY PROB OF SOME WATER ON THE FLOOR. I TURNED TO DISCUSS THE GALLEY PROB WITH MY FLT ATTENDANT. AFTER APPROX 2-3 MINS OF DISCUSSION; MY FO MADE THE COMMENT THAT IT TOOK AN AWFUL LOT OF PWR TO MAINTAIN AIRSPD. AS I TURNED BACK AROUND; I NOTICED HE HAD THE PWR LEVERS ALMOST FIREWALLED AND THE AIRSPD AT 210 KTS. AS I SCANNED THE INST PANEL; WE BOTH NOTICED THAT THE ACFT WAS CLBING THROUGH FL286. WE WERE 3600 FT ABOVE OUR ASSIGNED ALT. AN EMER DSCNT WAS MADE BACK TO OUR ASSIGNED ALT. ONCE WE LEVELED OFF; I ASKED HIM WHAT HAPPENED AND HE COULD NOT PROVIDE AN ANSWER. THE ACFT WAS ON AUTOPLT AND THE ALT HOLD SWITCH WAS OFF. HE DID STATE THAT HE WAS DISTR BY THE PROB I WAS WORKING WITH THE FLT ATTENDANT. I SUSPECT THAT; AS HE STARTED THE TURN OUTBOUND IN THE HOLDING PATTERN; HE TURNED IN HIS SEAT TO VIEW US AND INADVERTENTLY OVERRODE THE ALT SELECT MODE AND PULLED THE NOSE UP. AS HE NOTICED THE AIRSPD DECREASING; HE PUSHED THE PWR UP TO CORRECT AND DID NOT NOTICE THE ACFT CLBING. I DID NOT HEAR THE ALT ALERT HORN GO OFF; HOWEVER; IT DID WORK PROPERLY ON ALL SUBSEQUENT LEVELOFFS AND ALT CHANGES. I'M SURE IT WORKED; I JUST DID NOT HEAR IT. WE WERE THE SECOND ACFT IN HOLDING AND AT THE HIGHEST ASSIGNED ALT. SUPPLEMENTAL INFO FROM ACN 359724: I WAS TIRED AS WE HAD BEEN GETTING UP AT XG00 AM (HOME TIME) FOR EARLY SHOWS. I HAD GONE TO BED EARLY BOTH EVENINGS; XA00 PM; THIS WAS THE THIRD DAY OF A 4-DAY TRIP.