I would definitely start looking for another job. I would have started looking for another job a long time ago, one that's not an hour's drive from where you live! Unfortunately, we are long past the days where employers actually care about the health and well-being of their employees. Many states are employment at-will states and you can be fired without any reason. I live in an at-will state and lost two jobs because of untreated apnea. I worked in a call center and as long as we were receiving calls, I was fine. As soon as it got slow and no calls were coming in, I was gone in less than five minutes. I had been working for this company for several years and was one of the top performers before this started happening, but that didn't matter. I was a customer service specialist, which was basically one step below being a supervisor and I actually had more power than some supervisors in my department because I was more knowledgable then they were about the job and what it entailed. As long as I was doing a good job and making them money, I was employee of the month several times and won other awards and got lots of bonuses. As soon as I started having trouble, I wasn't making them money any more so I was out of there. I met with an attorney who specialized in employment law and she told me that I was basically SOL in this state, there was nothing I could do about it.
You're probably okay now because you're being treated, but you definitely need to get another job and get out of there. Unfortunately, that period of time where you had poor performance due to your illness will always be in your personnel file. If something else were to happen, they could go back to that and use it as an additional excuse. Get your resume updated and start pounding the sidewalk for another job! Good luck!