Following a stressful layover which provided neither rest nor proper nourishment; the Captain of a B767-300 returned to the departure gate when he became ill during taxi for takeoff.

Narrative

Our flight time for the day was a bit more than 10+00 while duty time was approximately 13+30. When I got to the hotel; I changed clothes and worked out. When I returned to my room; I showered and laid down to take a nap. When I awoke; the local time was approximately XA30. I watched T.V. and had some fruit for dinner. I was unable to sleep; so I remained awake until about XK00 in the morning; and ordered room service for breakfast. I had 2 poached eggs with toast and grapefruit juice. After breakfast; I showered and then laid down to sleep prior to our departure from the hotel which was set for XT00 local time. My rest was sporadic. I would sleep for a while and then wake up. I would then start the process again; and this continued up to my wake up time.We left at XT00 and proceeded to the airport. After arriving at the aircraft; the preflight was completed and I returned to the cockpit to prepare for our departure. We completed our checklists; received our ATC clearance; and completed our preparations for departure. As we taxied out; I began to feel sick at my stomach. I also began to feel tired. When the sickness and fatigue did not pass; I decided to return to the gate as this was the safest course of action. As we returned to the gate; the feelings of fatigue and sickness continued.When we arrived at the gate we secured the aircraft. After this had been accomplished; the sickness began to subside a bit and I went to change my shirt as we prepared to go back to the hotel. I left the aircraft; walked down the stairs; retrieved my luggage and boarded the crew bus to the terminal in order to clear Immigration. We then took the car to the hotel. During our ride to the hotel I still felt tired and sick at my stomach but it was not as intense as it had been earlier.After checking into my room I ate a candy bar from the mini bar and almost immediately began to feel better. I showered and laid down and slept for approximately five hours when I received a call to set up a physical here. I accomplished the physical and later flew back to the U.S on commercial flights. In retrospect; I believe that I had a low blood sugar event which was compounded by a lack of quality sleep. The breakfast I had was likely not enough to carry me through the day; and I had skipped lunch so that I might get a bit more rest. This was a mistake that I will not make again. Also; I believe that I slept too long during my nap; and this kept me awake through the evening thereby disrupting my sleep cycle for the coming day.