The pilot took off on a demonstration flight to familiarize the passengers with the helicopter. He reported that after takeoff, he proceeded northeast at about 100 to 150 ft AGL and 80 knots in wind that was from the west at 25 gusting 30 knots. After traveling about 3 miles, he turned left toward a westerly direction, using approximately a 30 degree bank. He stated that just prior to rolling out of the turn, the helicopter started to rapidly lose altitude and the forward and aft cyclic control would not respond to his inputs. Subsequently, the helicopter impacted the ground. He believed that the wind had shifted and the helicopter may have turned downwind and began settling with power. According to a passenger, when the helicopter was in the turn to the west, he felt a thump, the aircraft began climbing, then went into a 360 degree spin to the right. No preimpact or part failure or malfunction was found. The three servo actuators were tested and all three functioned properly. Local pilots reported the winds were often unpredictable due to rolling hills in the area.