A PA-46T pilot; distracted by personal concerns and an inquiring passenger programmed the wrong 'direct to' fix and failed to adjust his altimeter to QNE passing through FL180.

Narrative

NY Departure or Center cleared me direct to COL. I saw CYN in the flight plan and went direct to CYN. About 20-30 minutes thereafter I had another lapse. While climbing through FL180; I did not switch my altimeter to standard atmospheric pressure; 29.92'. When I leveled off at my interim assigned altitude of FL200; I was 400 FT high. When Center questioned my altitude I reported that I was at assigned altitude; then immediately realized my error.There was a considerable amount of stress prior to the flight. My wife was ill and unable to make the preplanned flight. I did not sleep well the night before. The combination of these factors impeded my ability to catch the fact that I initially was flying to the incorrect waypoint. Although I was aware that I was not functioning at my normal capability and thought that I was concentrating enough to overcome my substandard physical and mental state; apparently I was not.Another complication was that my son was on board. He has not flown with me recently and was asking a lot of questions that also created some distractions. I should have either canceled the flight or if not; then been more strict on sterile cockpit procedures.