I need a walker...

I was walking to work today, Zune in one hand, lunch bag and purse in the other. For no apparent reason, I just turned my ankle and went tumbling on to the sidewalk along Wisconsin Avenue. Of course because my hands were full I tried to just stumble rather than full-on fall, but all that did was just prolong my tumble. It was like it was in slow motion… I took a step to one side, then the other, all while my body was getting closer and closer to the pavement. Finally I just mentally said “screw it” and I fell on to the sidewalk. This little elderly lady was walking behind me and she scuttled over to see if I was okay. I had my headphones on so I couldn’t quite hear what she was saying, so I just said “I’m fine! I’m fine!” and continued on my way to work with a really skinned knee. What is wrong with me? The last two times I have fallen on the sidewalk, it has been for no reason at all… I’m just walking along and all of a sudden I fall.