You are doing the correct thing by telling your employer of your needs. I had a job about 10 years ago in which I specifically told them I had too much anxiety about answering phones (which was not what I was initially hired to do) but they kept making me do it. One day, I couldn't cope and asked a doctor to answer it for me. They fired me. Then they told me I agreed to take on reception duties on occasion at my interview. (to cover themselves). Jerks.