I had a Single Fiber EMG and a regular EMG many years ago when I was diagnosed with Myasthenia Gravis. From what I remember, the Single Fiber EMG was more painful because it took longer than the regular EMG. But it wasn't anything that I couldn't tolerate.
I hope the results will give you some idea as to what is going on. One of the hardest things to deal with is not knowing why you feel the way you do.