The power liftgate (automatic trunk) system on my 2019 Infiniti QX50 malfunctioned. After fully opening, the liftgate unexpectedly closed on its own without any warning beeps or resistance detection. This poses a severe safety risk. The heavy door struck my head, causing a physical injury (a severe bump/contusion). The vehicle and the affected components are available for inspection upon request. This problem has not yet been inspected, reproduced, or confirmed by a dealer, manufacturer, police, or insurance representatives, as I am reporting this dangerous safety defect immediately. Furthermore, there were no warning lamps, error messages, or any other symptoms prior to this sudden failure.