On July 6, 1997, at 1005 mountain daylight time, a Beech G35, N4552D, registered to and operated by the pilot as a 14 CFR Part 91 personal flight, ran off the side of the runway and nosed over during the landing roll at Jackson, Wyoming. Visual meteorological conditions prevailed at the time and no flight plan was filed. The airplane was substantially damaged and the airline transport pilot received serious injuries. The flight had departed from Worland, Wyoming, earlier in the day. In a written statement, the pilot reported that the flight originally began on July 3, 1997, from Poughkeepsie, New York. The first leg of the flight was from Poughkeepsie, NY to Findlay, OH, for a fuel stop, then onto Sioux Falls, SD. The pilot reported that the day's flight was 9 hours and 45 minutes of flight time in instrument meteorological conditions. On July 4, 1997, the pilot took off from Sioux Falls at 0927 in visual meteorological conditions and flew to Spearfish, SD. The flight duration was two hours and 30 minutes. On July 5, 1997, the pilot stated that he took off from Spearfish fairly early in the morning and flew at 12,500 feet to Jackson, WY, until he had to turn around due to heavy rainstorms. The pilot diverted to Worland, WY, and landed after two hours and 30 minutes in the air. The pilot stated that he did not have lunch that day and his dinner that night in Worland was "tasteless and unappetizing." On July 6, 1997, the pilot reported that he was up before daylight and called Flight Service for the weather for his flight to Jackson. The pilot was advised to get an early start due to thunderstorm activity over the mountains on the route to Jackson. The pilot stated that he did not have breakfast and was "painfully hungry" before he took off from Worland. After takeoff, the pilot climbed to 12,500 feet. The pilot stated that he felt hungry and weak, and when he tried to open the valve for the oxygen, his hand was too weak to open the valve. The pilot continued the flight and stated that he was confused about turning points, altitudes, distances, and he felt "woosy." As the flight approached the Jackson area, the pilot maneuvered for landing, and had stated that he had difficulty determining pattern altitude and staying awake. The pilot stated that he put the flaps down on final approach and was continuing to have difficulty staying awake. The pilot noticed that he was low on final, and stated that with great difficulty, he pushed the throttle forward. The pilot stated that as the airplane crossed over the end of the runway, he felt that he was half asleep and not doing anything to control the airplane. The airplane landed hard and turned off to the left and exited the side of the runway. The pilot stated that the throttle was still open and he could not figure out why he was not slowing down. Finally the nose gear collapsed and the airplane nosed over. Witnesses reported that the airplane touched down very fast and then veered off the side of the runway. The witnesses who were the first to arrive at the accident site and who assisted the pilot in evacuating the airplane, reported that the pilot was disoriented and appeared "hypoxic." When the pilot was asked if he had been using oxygen, the pilot reported that he had been flying at 12,500 and that he couldn't reach the oxygen while in flight.