Shoes, Chair and Feelings of inadequacy

My job was not boring, not by any means. But the constant stream of customers terrified me. Mostly because I didn't know how to answer their questions. There were other things too. I have never been in any sort of a professional environment. I didn't know how to behave with my colleagues. Should I be friendly? Should I be a professional and talk to them only about work? How should I react when one of them makes a joke? Also, I felt continuously apologetic for my ignorance and incompetence. Everyone else worked so hard all day long. I just sat on a chair and pretended to be busy, but in reality, I was as much useful as a band-aid on broken leg. I felt so awful about that, I can't even begin to describe. Once I went to kitchen and scrubbed the surface of the slab just to contribute in any way I could. I had never known that being unuseful could cause so much despair. There were other problems too- the chair and the shoes. The chair swivelled too much and my sneakers slipped on the shiny floor all the time... I was constantly afraid of falling down in front of customers and make myself the butt of jokes for the rest of the month. One day my worst fear came true... I was sitting on a chair and sort of leaning onto another empty chair, when my colleague Finny called me to pass him a pen, I took my hands off the chair to grab the pen, and immediately fell ass-first on the floor. I hurt my backside pretty hard, but couldn't rub it or anything. I only fell one more time in the branch. But it was a whole different kind of falling.