According to the pilot, the previous day he awoke about 0700, and went on duty at 1800. About 1930, he flew the helicopter on a 1-hour flight and attempted to take a nap at 2100. The nap was interrupted with noise and lights constantly being turned on and off, and he accrued no more than 1 hour of rest. At 0030, on the morning of the accident, he was called to fly for the purpose of frost mitigation. About 0540, while flying over an agricultural field about 30 feet above ground level, he began his last pass over the field, and "fell asleep." Subsequently, the helicopter impacted the ground and came to rest on its left side resulting in substantial damage to the fuselage, rotor system, and tail boom. An examination of the wreckage by a Federal Aviation Administration inspector revealed there were no mechanical anomalies with the helicopter. At the time of the accident the pilot had no more than 1 hour of restless sleep in the previous 22 hours 40 minutes. The pilot also reported that he did not normally fly at night.