My aunt had the same problem. The doctors diagnosed it as PD. She will be okay most of the time but when she starts to walk after a few minutes she will start to fall. We even bought her a emergency necklace form Toronto
so that she can sound the bell if no one is nearby. Thankfully that never happened. Then after 5-6 months it cured automatically. She can now walk steadily without any problem. This PD is a very curious decease.