SINGLE PLT OP. PLT LEFT THE COCKPIT FOR PHYSIOLOGICAL REASONS LEAVING PAX (WIFE) IN THE COCKPIT. AUTOPLT DISCONNECT BUTTON PUSHED INSTEAD OF MIKE SWITCH RESULTING IN EXCURSION FROM ASSIGNED ALT AND A 2-G RECOVERY BY NON PLT WIFE.

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WHILE CRUISING ON ALT AND NAV; AUTOPLT AT 9000 FT IFR IN MOSTLY IMC CONDITIONS; I HAD TO LEAVE MY SEAT FOR PHYSIOLOGICAL RELIEF. THE PAX IN THE COPLT SEAT (MY WIFE) HAS ACCOMPANIED ME ON APPROX 100 HRS OF XCOUNTRY FLT IN VARIOUS SINGLE- AND MULTI-ENG ACFT. I ASKED HER IF SHE WOULD ANSWER THE RADIO IF CTR CALLED WITH A FREQ CHANGE. SHE SAID NO; SINCE SHE IS NERVOUS ABOUT MAKING RADIO CALLS. I INFORMED ZTL THAT I WOULD NEED TO BE OFF FREQ FOR 2 MINS AND I'D RPT BACK ON. THAT WAS APPROVED. WHILE I WAS IN THE BACK OF THE AIRPLANE AT THE URINAL; ZTL CALLED TO SEE IF I WAS BACK ON FREQ YET. THE PAX IN THE COPLT SEAT THOUGHT SHE WOULD ANSWER THE RADIO CALL AND TELL THEM I WASN'T BACK YET. SHE REACHED ACROSS AND PUSHED WHAT SHE THOUGHT WAS THE PUSH-TO-TALK SWITCH ON MY YOKE. SHE HAD ACTUALLY PUSHED THE AUTOPLT DISCONNECT SWITCH ON MY YOKE. AT THAT TIME A PAX IN THE BACK OF THE AIRPLANE ASKED MY WIFE A QUESTION. MY WIFE TURNED AROUND AND SPOKE WITH THE OTHER PAX FOR A MOMENT. WHEN MY WIFE TURNED FORWARD SHE SAW THAT THE ACFT WAS IN A DSNDING TURN. I WAS ON MY WAY BACK UP TO THE COCKPIT WHEN SHE PULLED BACK ON THE YOKE AND LEVELED THE WINGS. I WAS FORCED TO THE FLOOR WHEN HER PULLBACK RESULTED IN APPROX 2 G'S. IN A COUPLE OF SECONDS SHE EASED THE BACK PRESSURE AND I WAS ABLE TO RETURN TO THE COCKPIT AND CORRECT THE ALT AND HDG DEVS.