Can I be fired if I am not the friendliest co-worker to work with?

Here's the deal, I have been on anxiety medication for 3 years now (major personal family issues, death, taking care of an elderly parent just to name a few). A few months ago to protect myself, I requested from my doctor's office a note signed by my physician of my anxiety issues as well as the medications I am taking. Most of the time, I am friendly and my work as I have been told is outstanding. However, I work with a few people who are not as knowledgeable as I am. So my answers to some of their questions are short. So a couple of people (widespread mostly internal phone calls) have complained about my attitude. That I am short with them and rude. Like I am being bothered one co-worker says. I gave this doctor's note to my HR Representative to have on file. If my attitude improves then fine there is no issue. But if it doesn't, it could lead to my termination. If that happens, do I have a legal right to obtain a lawyer and sue my employer?