What Causes Imbalance Of Body In An Elderly Person?

For the past three years I have had stability problems. Now I always hold onto a railing whenever I go up or down a staircase. Even when I walk along a level walk I don't feel very stable. In the past year I have fallen down three times. The first time it took me at least twenty minutes before I was able to get up, and then only because I had a handrail nearby. I am 77 years old and consider myself as being in good condition. I never smoke or drink but I do take Lisinopril for high blood pressure and Clonazepam for anxiety.