Shortly after takeoff from an off-shore platform at night, the helicopter entered a series of extreme pitch excursions which resulted in the airspeed reducing below 20 kt, followed by a descent. The flight crew were eventually able to recover to normal flight. The helicopter had descended to within approximately 50 feet of the sea surface. It was found that the helicopter’s flight path was consistent with inappropriate control inputs. The investigation concluded that a combination of technical and organisational factors had pre-disposed the flight crew to believing that the helicopter was not performing correctly, which led them to depart from normal operating parameters. This resulted in the crew rapidly becoming disorientated to the extent that their ability to control the helicopter safely was compromised. Several safety actions have been taken by the helicopter operator.