On June 5, 1998, about 1445 eastern daylight time, a homebuilt Rotorway International Executive 162F helicopter, N162WM, registered to a private individual, rolled over after touchdown at the Hidden Lake Airport, New Port Richey, Florida. Visual meteorological conditions prevailed at the time and no flight plan was filed for the 14 CFR Part 91 instructional flight. The helicopter was substantially damaged and the student pilot and one passenger were not injured. The flight originated on the airport about 20 minutes earlier. The pilot stated that the purpose of the flight was to practice hovering with a passenger on board in preparation for an upcoming checkride. He had been practicing hovering for about 20 minutes when, while flying about 4-5 feet agl at 4-5 mph over a creek, he noted that the main rotor rpm decayed. He lowered collective and attempted to accelerate, but the skids contacted the ground and the helicopter rolled onto its right side. He further stated that there was no engine or airframe malfunction and contributing to the accident was the fact that he had only obtained 2-3 hours rest for each of the past 4 nights.